The Hockey Stick Effect: Wayne Gretzky’s Goals, Part 1

1 Apr

What is the measure of greatness? How about 894 records, one for each of the goals driven home by the National Hockey League’s Wayne Gretzky, aka the Great one?

That spreadsheet is as large as it gets for NHL scorers, and Tableau ace Ben Jones has infused the goal count with lots of supplementary background about each and every one of the 894, archiving the data for download on the data.world site here.

In fact the workbook makes itself available in both Excel and CSV mode, the latter requiring a text-to-columns parsing that likens it to the former. Either way, a few organizational points need to be entered.

For one thing, you’ll note that what’s called the Rank field in column A numerically ids Gretzky’s goals, in effect sorting them by newest to oldest. That is, Gretzky’s first goal – scored on October 14, 1979 – has received id 894, with the numbers decrementing ahead in time until his final score – tallied almost exactly 20 years ago on March 29, 1999 – has bottomed out with the number 1. It seems to me – and I suspect you’ll share the opinion – that the enumeration should have pulled in the opposite direction, with Gretzky’s last goal more properly checking in at 894. With that determination in mind I reversed the sequence via a standard autofill, entering 894 in cell A2, 893 in A3, and copying down.

You’ll also be struck by the unremittingly monotonic entries in the Scorer field, comprising 894 iterations of the name Wayne Gretzky. We’ve seen this before in other data sets, of course, being dragged into the data set as a likely accessory to some generic download protocol. Again, you can either ignore the field or delete it. Either way, you’re not going to use it.

And your curiosity will be stirred anew by the blank column-heading cells idling atop columns D, F, and G. It’s difficult to believe that Ben Jones, who doubtless knows whereof he speaks, would allow these most rudimentary oversights to escape his notice, but alternative explanations notwithstanding, the headings aren’t there and must be supplied.

Column D reports a binary datum – whether a Gretzky goal was scored at his team’s arena or at the rink to which his team traveled for an away game. I’ll thus entitle the field Home/Away and proceed to do something about the data themselves, whose cells remain empty when signifying a home goal and register an @ for “at”, that is, a goal netted at someone else’s arena. A pair of finds and replaces – the first, substituting an H for the blank cells, with the second supplanting the @ signs with a companion, alphabetized A – should sharpen the field’s intelligibility.

The headless column F archives game outcomes, i.e. wins, losses, or ties, and so I’ll call the field Result, or something like it. Column G denotes the phase of a game when the goal was scored, either during regulation time or overtime – or so I assumed. But a second thought soon followed on the heels of that hunch, if I may mangle the metaphor: it occurred to me that the Regulation/Overtime opposition simply recalls whether or not the game itself swung into an overtime period, irrespective of the actual times at which Gretzky scored. Could that uncertainty be relieved?

I think so, and I played it this way: first, I named the doubtful field Reg/OT, and ran a find and replace at the F column, substituting Reg for any empty cell therein. I then moved toward a pivot table:

Row Labels: Date (ungrouped, in order to exhibit each date)

Columns: Reg/OT

Values: Date (Count)

What I found is that no game date featured a value for both a regulation and overtime goal, a discovery that goes quite some way toward clinching the second speculation – namely, that the Reg/OT field entries do no more than inform us if the games necessitated an overtime period.

After all, if we confine the analysis momentarily to the games that spilled into overtime, one could most reasonably imagine that a scorer with Gretzky’s gifts would have occasionally lodged a goal in both the regulation and overtime phases of the same game; but the pivot table uncovers no such evidence. For any given date, Gretzky’s score(s) appear in either the OT or the Reg column. Moreover, some of the games – for example, November 27, 1985 – record two overtime goals, a unicorn-like impossibility in a sport in which overtime ends when the first goal is scored. (You’ll note by the way that the overtime-column goals only begin to appear in 1983, when a five-minute overtime period was instituted.)

Thus I’d aver that the Reg/OT field conveys little understanding of Gretzky’s scoring proclivities; all it does is identify games that happened to have extended themselves into overtime, and in which he scored – some time.

The Strength field cites the demographic possibilities under which Gretzky accrued his goals: EV refers to even strength, when both teams’ numeric complements on ice were equal, PP, or power play, during which the scoring team team temporarily outnumbered the other after a player was remanded to the penalty box, and SH or shorthanded, the rarest eventuality – when Gretzky scored while his team was outnumbered.

I do not, however, know with certainty what the EN entry in the Other field represents even though I probably should, and I see nothing in Data World’s data dictionary that moves to define it. It may very well stand for end, as in end of game, however; each of its 56 instances are joined to goals there were scored with fewer than two minutes left in their respective games. EN may then stand for scores achieved after the opposing goalie skated off in a losing cause and was replaced by offensive player, in order to buttress a desperate try at equalizing the game. Indeed – all 56 of the EN goals were scored in wins by Gretzky’s team.

As a matter of fact, I think I’m right. Filter the Other field for its ENs and look leftward at the Goalie field in L. There’s nothing there.

U.S. State Dept. Travel Advisories: Getting There

17 Mar

First principles: before you subject a dataset to your imposing, if caffeinated, spreadsheet acumen you have to actually get the data. But that blitheringly obvious stipulation is, nevertheless, sometimes easier stated than achieved.

It’s true that most open data sites aim to please and affably release their holdings, via a tick of a well-placed and intelligible Download or Export button, or something like it. But there is a particular brand of spreadsheet manqué that issues its data in stages – that is, it mothballs them across several web pages, and not then in a unitary place.

That segmented storage strategy might enhance the data’s readability, or might not, though if nothing else the multipage design spares viewers from scrolling relentlessly down the page. My question about these kinds of datasets is simple: can they be downloaded directly into a single spreadsheet without contortion?

And that question placed itself before me anew a short while ago when I met up with the US Department of State’s travel advisory dataset, brought to my attention by the Far and Wide site. That dataset looks like this, necessarily in part, given its multi-page distribution:

travel 1a

The set’s three fields seem perfectly limpid (save perhaps the Worldwide Caution entry, which appears to commend a global, and not a country-specific advisory); but their data are spread across five pages, each of which must be clicked separately:

travel5

Yes; as earlier indicated, It’s one of those kinds of datasets. And again – can I get it all into my spreadsheet without that most unbecoming of resorts: five copy-and-pastes, rife with pinched column widths and text that needs to be unwrapped? (Note by the way that as of this writing New Zealand’s Level 1 assessment I the data set hadn’t changed, having been last updated on November 15 2018. However, an alert for the country has been entered here.)

When assailed by such questions, a hopeful right-click upon the data gives us nothing to lose and something, perhaps, to gain e.g.

travel6

The third option from the bottom looks promising. Click there and we’re told that the data before us will find their way into my waiting spreadsheet. But I seem to recall having viewed that Export instruction elsewhere on other sites, with decidedly mixed results.

But why not. I gave it a click and to my surprise observed something actually happening on my blank worksheet, an ellipsis-freighted “External Data_1: Getting Data…” message that deliberated on screen for several minutes before finally giving way to an actual, unitary spreadsheet, e.g.

travel2

In other words, the export actually exported. Note that the advisory data in column A appears on site in a stream of hyperlinks that when clicked directs the viewer to a deeper background on the country in question; presumably the export routine thus executes a Paste Values protocol that strips the records of their more exotic contents. On the other hand, the download did introduce the Date Updated field to the spreadsheet in actual, numerically viable date mode.

So it worked, to my pleasant surprise, though a few significant qualifications of the process need be entered. First, a right-click on the first, Advisory field did not summon the Export to Microsoft Excel option; it was only when I attempted a click over the second or third field that the context menu disclosed the command. Second, and perhaps most importantly, the Export possibility only seems to make itself available when the sites are broached with Internet Explorer. Attempts to coax Export from the menu in the course of perusals conducted in Chrome or Firebox failed, and I am presently unaware of an enabling workaround for either browser, though I am happy to be reeducated on this count.

Now of course Excel and Internet Explorer spring from the same shop in Redmond, and so one could be left to draw one’s own conclusions on the matter. Is this what they mean by “seamless integration”? Seamless, but unseemly? I don’t know.

In any case, my success with the export fired up the obvious follow-on question: could the deed be replicated with similar datasets thronging the internet?

In search of answer, I stopped off at the US News and World Report rankings of law schools and clicked its Table View button, assuming that something like a spreadsheet would eventuate as a consequence. Once in view I again right-clicked the data’s second, Tuition field, revisited Export to Microsoft Excel (remember, I’m back in Internet Explorer), and was delivered this compendium (in excerpt):

travel3

While the above tableau and its quiver of alternating blank rows won’t pass Spreadsheet Design 101 (and I’m an easy grader), the “fault”, if I may be so judgmental, lies with the site and not the export, which seems to have captured the data as they appear on site. In short, the export seems to have worked again.

In the interests of building up a scientifically workable sample I turned next (again in Explorer) to the Times Higher Education world university rankings, which look something like this it situ:

travel4

Again, a right click upon the data ushered Export to Microsoft Excel to view (though the command appeared after clicking either the data’s first and third fields, but not the second), but this time the spreadsheet registered nothing but a companionless header row for the rankings. I retried the export numerous times, but met with the identical result on each attempt.

I can’t explain the discrepancy, i.e. why some data sets comply with the export request and others resist. That’s not to say an explanation can’t be adduced, of course, but I’ll have to assign that accounting to a web programmer. Clearly, the kinds of data tropes we’ve reviewed here embody a different genotype from that inherited by the standard open-data-site collections we usually confront here, those designed in large measure to download immediately into spreadsheets; and while it’s true that these web-emplaced data are probably meant to facilitate searches for a particular item and little more, it might be a good idea for their designers to anticipate the prospect that someone out there might wish to analyze the whole lot, and by treating the data as a whole, and seeing to it that they find their target in a spreadsheet all the time.

Screen Shots: Charting Movie Ratings

1 Mar

Granted; the line between an iconoclast and a smart aleck is but a few pixels wide, and so it’s not impossible to plant one foot on either side of the characterological divide. And while I’m straddling that gossamer border I’ll voice the notion, something at which I’ve hinted before: that Excel can do some things that other people do by mustering what feels like heavier artillery. That is, even as some practitioners of the programming arts unleash charts and vizzes of no mean quality upon their blogs, I’ll suggest in a whisper that highly reasonable facsimiles of the above can be emulated by Excel.

I’ve intimated as much before, e.g. my previous post, wherein I framed a scatter plot dotting NBA players’ offensive-to-defensive margins that successfully (if I do say so myself) imitated the chart synthesized by a corps of programmers applying a language or two (ggplot2) to the task. You may also recall my Excel-driven approximation of the celebrated charts of disease eradication here; and now I’m at it again.

My model this time is the chart shaped by the graphics adepts at the BBC that positions the respective film ratings of critics and viewers of 2017 Oscar-nominated films, e.g in excerpt:

movie1

Audience evaluations are captured by the red dot with the greenish speck symbolizing aggregated critics’ scores, and the interposing gray bar conveying the scope of the discrepancy between the two assessments.

It’s a neat representation, one redolent of the controls you’d slide across this or that hi-tech contraption, though of course – excuse the iconoclasm – you could ask if the above visualization delivers its message more crisply than an off-the-shelf, industry-standard column chart that treats each film to a pair of comparative bars.

But that judgement aside, a surmise followed on: could I do something similar in Excel? I suspect you know the answer.

First, the data, which was gleaned from the Metacritic site that compiles review scores. Not being able to contrive out how to access these directly I simply transcribed the numbers from screen shots of the two sheets bearing the figures, e.g.

movie2

There are indeed two sheets – one reporting movies having received relatively more favorable critic ratings, the other enumerating the ones for which audience scores were the higher. In practice for our purposes, of course, only one sheet is required; there’s no operational reason for parting the sheets on the basis of the critic/audience margins.

Moreover and as you see, the screen shots feature the critic/audience rating gap for the movies, a differential that, for our charting intentions, is irrelevant. After all, the intervening gray bar should portray those differences as a matter of course (it appears by the way that some of the critic-preferred subtractive differences aren’t quite correct).

For the sake of demonstration I then simply transcribed the data onto a spreadsheet for 20 records (say A4:C24, reserving the top row for headers) – ten in which critics’ estimations topped the popular appraisals and ten in which the support trended the other way, and rounding off the numbers when required in the interests of demo simplicity.

I then selected D5:CY5 – thus bridging the 100 columns following C and so making room for any potential audience/critic rating – and proceeded to clip their widths to .42 (a measure on which you may want to experiment), and entered in D5:

=IF(OR($B5=COLUMN(D5)-3,$C5=COLUMN(D5)-3),CHAR(149),0)

What is this formula doing? First, it needs to subtract 3 from each column reference (COLUMN identifies the column number of a reference, e.g. =COLUMN(D4) returns 4) in order to for D5:CZ5 to span values 1 through 100. It then asks if a given cell’s column value equates to the film rating stored in either B5 or C5; if so, the qualifying cell(s) (one of which should satisfy the stipulation in B5, the other in C5) installs a dot, via the CHAR(149) expression, the character number for that symbol in Calibri. And that’s a dot, not a sentence-capping period. (Note that I’ve elected to size the dots to 13 pts, given the column widths, a reading you may want to tweak.) I then copied the formula across D5:CY5.

In view of the tact that my first film – the one I recorded in row 5, Warcraft – received an average 38 ranking from critics and a boffo 82 from filmgoers, the dots should instate themselves in positions 38 and 82 – in default black. A hip color, perhaps, but we want to emulate the green and red buttons the BBC set forth – the green for the audience rating, and red for the critics’ assay. That sounds like a job for a couple of conditional formats; and so after selecting D5:CY I can write

movie3

and

movie4

These expressions ask if any cell falling within D5 and CY5 equals the value in B5 – the critics’ rating – or C5, that of the general viewers. If the former condition is met the dot turns the critics’ red; fulfillment of the latter logical test colors the dot green. Note that because the CHAR(149) realizes a textual result – that is, the dot is just that and not a conditional formatting icon – the conditional format invokes a font color change.

Now we next need to engineer the gray band that connects the dots, as it were. I selected D5:CY5, and fired up another conditional format formula:

=AND(COLUMN(D5)-3>MIN($B5:$C5),COLUMN(D5)-3<MAX($B5:$C5))

The AND statement looks for cells whose column values register a number between the respective critic and audience ratings. Cells that conform to the criteria receive a gray fill color.

And all that means that the charted scores for Warcraft look like this:

movie5

Not too bad, but I’m biased.

If you’re happy with that take, you can copy the contents of D5:CY5 down through the other films, a move that’ll bring the conditional formats along with them. Next, in the interests of presentational clarity, I’d insert a blank row between each pair of films. (If that stratagem sounds slightly tedious, see this alternative that might or might meet with your approval.)

That chore attended to, the ratings start to look something like this:

movie6

I think it’s ready for release; I may submit it to Metacritic, in fact. I, for one, give it an 84.

NBA Field Goal Data, Part 2: More Than 3 Points to Make

11 Feb

Among the metrics figured and plotted by the Medium look at NBA shot-making (and missing) is a two-way-player analysis, a comparison of the points scored by a given player to the points surrendered in his defensive capacity. As the study authors allow, the measure’s validity need be qualified by several cautions, e.g. the fact that an offensive dynamo might be assigned to guard a scorer of lesser prowess, thus padding his points differential. In any case, we can ask how a spreadsheet might applied to the task.

And that task is encouraged by the data’s CLOSEST_DEFENDER field, which identifies the player nearest a shooter at the point when he launched the shot. Thus by totalling a player’s points and subtracting the sum scored “against” him in his closest-defender role, the metric is realized. (Remember that the data issue from three-quarters of the games comprising the 2014-15 season.) But in view of the way in which the data present themselves, calculating that difference is far from straightforward.

It’s simple enough to drop this pivot table into the equation:

Rows: player_id

player_name

Values: PTS

That resultant – indubitably straightforward – apprises us of the number of points (scored via field goals, but not foul shots) credited to each player, and we’ve earmarked player_id here for inclusion in the table in order to play the standard defense against the prospect of multiple players with identical names. (Subsidiary point, one that’s been confronting my uncomprehending gaze for quite some time: fashioning a pivot table in tabular layout mode substitutes the actual data source field names in the header for those dull “Row Label” defaults. Thanks to Barbara and her How to Excel at Excel newsletter.)

But it turns out that an another, data-set-specific requirement for player_id imposes itself on the process. In fact, the player names in CLOSEST_DEFENDER are ordered last name first, surname distanced from the first by a comma, Yet the entries in player_name hew to the conventional first name/surname protocol, daubing a viscous blob between the two fields. Excuse the pun, but properly comparing the fields would call for a round of hoop-jumping that won’t propel me off my couch – not when I can make a far simpler resort to both player_id and CLOSEST_DEFENDER_PLAYER_ID, which should encourage a more useful match-up (but I can’t account for the mixed caps/lower-case usages spread across the field headings).

That understanding in tow, we can plot a second pivot table, one I’ve positioned on the same sheet as its predecessor, set down in the same row:

Rows: CLOSEST_DEFENDER_PLAYER_ID

Values:  PTS

The paired tables should look something like this, in excerpt:

nba21

Once you’ve gotten this far you may be lightly jarred by an additional curiosity scattered across the data: namely, that the closest defender outcomes comprise far more players, a few more hundred, in actuality. I looked at the stats for two of the players who appear in CLOSEST_DEFENDER_PLAYER_ID only – ids 1737 and 1882, i.e. Nazr Mohammed and Elton Brand, and learned that their offensive stats for 2014-15 were rather sparse (check out www.basketball-reference.com for the data); Mohammed averaged 1.3 shots per game that years, with Brand checking in at 2.6. It may be, then, that the data compilers decided to omit field goal stats for players falling beneath an operationalized threshold, but that conjecture is precisely that.

You may also wonder why two pivot tables need to be impressed into service, when both train their aggregating gaze at the same PTS field. It’s because we’re directed different parameters to the respective Row Label areas – one identifying the scorers, the other naming what are in effect the same players but in their capacity of defender, there lined up with someone else’s points, so to speak.

In any case, once we’ve established the tables, we can dash off a column of relatively simple lookup formulas alongside the first pivot table, one that searches for the equivalent player id in the second. I’ve named the data range in the second table defense, and can enter, assuming the first receiving cell is stationed in A4 (I’ve named the budding field Points Surrendered in A3. Remember of course that the field is external to the actual pivot table):

=VLOOKUP(A4,defense,2,FALSE)

And copy down the column.

(The FALSE argument is probably unnecessary, as the ids in both pivot tables should have been sorted as a matter of course.)

The lookups track down the ids of the players listed in the first pivot table, and grab their points surrendered totals, culminating in a joint scenario resembling this shot in excerpt:

nba22

And once engineered you can, among other things, subject the lookup results to a simple subtractive relation with the sum of pts to develop the offense/defense differential on which the Medium piece reports. You could also divide players’ points by points surrendered instead, developing a ratio that would look past absolute point totals.

Remember, however, that Point Surrendered “field” and the suggested follow-on formulas are grafts alongside, but not concomitant to, the pivot table, and as such you could unify all the fields’ status by selecting the first pivot table and running a Copy > Paste Values upon the results, thereby sieving the pivot data into a simple data set now of a piece with Points Surrendered and kindred formulas.

If we go ahead and divide pts by points surrendered and sort the results highest to lowest we see, in excerpt:

nba23

The findings are both interesting and cautionary.  Dwayne Wade’s and Lebron James’ enormous differentials may have more to do with their offensive puissance than their preventive talents, offset by the understanding, on the other hand, that a good offense may well be the best defense. What’s really needed, however, is a finer scrutiny of the players to which they’ve been assigned – and the same could be said about those who cede far more points than they score on the other end of the sort.

Of course, with all those parameters there’s no shortage of looks you can cast at the data. For example, try this pivot table:

Rows:  CLOSEST_DEFENDER

CLOSEST_DEFENDER_PLAYER_ID

Values: PTS

ShotPct (the calculated field we hammered together in the previous post).

I get in excerpt:

nba24

The intent here is to compare players’ points surrendered – an absolute measure – and the shooting percentages of the players they’ve guarded. Scan the list and you’ll see that Lebron James “held” his shooters to a middling .442 percentage, but Dwayne Wade restricted his opponents to a .394 mark, suggesting his defensive goods are for real. But again – the numbers need to be checked against the overall percentages of shooters. It may be that Mr. Wade has been issued a light workload.

And for a concluding, graphical touch, the Medium piece offers a scatter plot pairing players’ points scored by and against:

nba25

I don’t know with what tool the authors plied the chart, but I very much doubt it was Excel. In any case I managed to achieve something very similar with that application:

nba26

How? Well first, recognize that Excel simply can’t put together a scatter plot from a pivot table. If you try, you’ll be told “Please select a different chart type, or copy the data outside the Pivot Table.”

Opted for the latter counsel, I copied these data, for example:

nba27

And pasted them into a blank sheet area via Copy > Paste Values. I then selected the two columns of data, and headed toward Insert > Insert Scatter (X, Y) or Bubble Chart (to add data labels, see this You Tube video).

I did all this stuff without a programming language in sight. Does that make me a philistine?

 

NBA Field Goal Data, Part 1: More Than 3 Points to Make

21 Jan

Spreadsheets can’t do everything, but don’t sell them short; there’s plenty a spreadsheet can teach us about the National Basketball Association shot data garnered by Kaggle right here, even though the data have already been vetted with some due diligence by the appropriately five-to-a-side team of Michael Arthur, Caleb Johnson, Aimun Khan, Nimay Kumar, and Reid Wyde in this look, shaking and baking on the Medium web site. The authors learned much from the sheet and its 128,000 records of player j’s, hooks, and jams, with particular reference to the vaunted, if mythical, hot hand – the perceived, stepped-up likelihood that any given shot finding nothing but net will somehow inspire the next one to make the same discovery.

That’s something we can look at, too, along with a number of other analytical scenarios we can fold into our playbook.

But first a few words about the data, which, as the above-linked piece allows, were in fact accumulated for the 2014-15 season (owing to availability issues for subsequent years).  In addition, the 30 NBA teams play an 82-game season, or an aggregate of 1230 unique contests; yet the dataset’s GAME_ID field carries 904 game identifiers, affirming a shortfall of about one-quarter of all the games that actually took the floor. I can’t account for the fractional representation, but those are the data we have. You may also want to think, and do something, about the GAME_CLOCK field, whose times mistakenly offer themselves in hour/minute format when they really mean minutes and seconds. The first entry, expressed as 1:09 AM, really wants to archive one minute and nine seconds, and so if you want to work with these data you may need to reach for a recalibration (remember that each quarter in the NBA extends for 12 minutes), which could entail breaking open a new temporary column alongside GAME_CLOCK, subjecting it to the mm:ss Custom format, and entering in what is now I2:

=H2/60

Because of course an hour comprises 60 minutes, dividing what are the hourly totals in GAME_CLOCK (ignore the AM suffix) by 60 miniaturizes the values to minute/second magnitudes. Once you copy the formula down I you can copy those outcomes back to GAME_CLOCK via the Paste > Values protocol and send column I back to the bench – and make sure GAME_CLOCK assumes the mm:ss Custom format, too.

That conversion having been plied, we can proceed to and get past the time-honored column auto-fit exercise and then begin to run-and-gun some actual questions at the data, including variations on the themes drawn by the Medium study. One such question asks about league shooting percentages, varied by what the authors term “areas of the [playing] floor”, a slightly misinforming alias for what are in fact distances from the basket, whose data in feet register themselves in the SHOT_DIST field. In fact a given distance can be fixed at any number of positions on a semi-circumference on the floor, e.g. the foul line or another point nearer the floor perimeter, even as both are plotted 15 feet from the backboard, for example. Two different “areas”, then, same distance. In any case, we could ask if shooting percentages push downwards with increased distance from the hoop. Common sense of course suggests they do, but proof awaits.

And here the Medium study performs something of a personnel substitution, by  turning to a new dataset for the shot-distance data (which again were gathered from the 2014-15 season) – even as it seems to me that those data could have been derived from the Kaggle workbook via its SHOT_DIST field. (In addition, the NBA data linked in this paragraph offer data for the entire 2014-15 season, disrupting a precise like-for-like comparison of our data which again report the numbers for but three-quarters of the year).

I can think of two or three means toward a shot percentage-by distance set of answers, the first cooking up a messy stew of FREQUENCY and COUNTIFS formulas, the second a relatively more elegant pivot table that necessitates an important tweak just the same.

Remember we’re interested in correlating shooting percentages with distance from the basket, and as such we could try

Rows: SHOT_DIST (grouped by units of 5 feet)

Values:  FGM (stands for Field Goals Made, Sum)

FGM (again, this time Count)

We want Count for that second invocation of FGM, because a counting of all the elements in the field- the 1’s for shots made and the 0’s for those missed – delivers the total of all shots attempted.

I get:

nba1

Note first of all the presentational imprecision besetting the row labels, by which the upper number in each bin is reprised in the lower value for the bin that follows. The numerical actuality imputes the accurate reading to the lower value, e.g. the first bin really tops out at 4.9 feet, and all truly five-foot shots contribute to the second bin. Remember, though, that you can hand-modify the labels, in the service of clarification, for example:

nba2

(Note also that the grouping by 5 really builds bins comprising six values, e.g. 0 through 5.)

But aesthetics aside, we still need to calculate the respective shooting percentages binned by those grouped distances – a simple mathematical proposition by itself, asking us merely to divide field goals made by field goals attempted. That intention sounds like a call for a calculated formula that could look something like this:

nba3

But guess what – as Excel savant Debra Dalgleish reminds me, calculated fields work exclusively with summed fields; try sneaking a COUNT in there and that nice try will be rejected.

A second suggestion, this one external to the pivot table proper, would be to compose a simple formula alongside the pivot table, e.g. =B4/C4 for the first bin, and copy it down, each formula sidling its bin. That’ll work, but if you regroup the data by a new interval, say 10 feet, the pivot table’s now-fewer rows will kick up a clutch of #DIV/0! errors that cling to the now-existent bins.

But this next alternative seems to work, even if it’s redolent of a kludge: make room for a new column in the dataset (say alongside FGM in S), call it something like ShotsAttempted, enter a 1 in S2, and copy that meek value down the column. What’s this curious maneuver doing? Glad you asked. It enables this calculated field:

nba4

ShotsAttempted’s endless litany of 1’s will be summed, and will divide themselves into the FGM values and break out by SHOT_DIST in Row Labels. Format appropriately (I tried a Custom format keyed to the .000 motif) and you’ll get something like this:

nba5

(Note that the Values area need only consist of the calculated field results.)

Of course the surpassingly high field goal percentage for shots in the 0-5 feet range won’t surprise (a zero-foot shot is presumably a dunk or a layup); what’s at least slightly surprising is that once shooters move out beyond five feet, the percentages sink markedly, in part at least a function of the more assiduous defense applied to the shooters out there. After all, if you’re positioned to dunk the ball you’ve already lost the man assigned to guard you (I cannot speak first-hand, you understand). Indeed – the aggregate shooting percentage for shots equaling or exceeding five feet is .393.

And once you’ve made your way this far into the analysis you can select the pivot table, copy it, and perform a Paste > Values nearby, thus establishing a fixed individual player baseline. Then draw up a Slicer earmarking the player_name field, and you can check out your favorite hoopster’s percentages by distance, e.g.

nba6

Moral of the story: don’t let Lebron get too close to the basket – nudge him out past 25 feet. At least that’s what I try to do with him.

New York City Restaurant Inspection Data: Tips Included

9 Jan

Expressing an interest in getting a bite to eat in New York calls for a bit of narrowing down. You will need to get a little more specific about your preferences, in light of the 26,000 or so restaurants in the city happy to fill your mouth, and evacuate your wallet.

Indeed – advising your New York crew “Let’s go to a restaurant” reminds me of the woman who stood in front of me in a Starbucks and requested a cup of coffee, the kind of order that drives baristas into a hand-crafted frenzy.

But once you’ve finally sat yourselves down you may want to learn a little more about what exactly it is you’ve gotten yourself into – literally – and the restaurant inspection data reorganized by the Enigma public data site may go a ways towards telling you more than you wanted to know (the data are free to you, but they want you to sign up first. Remember that the lower the inspection score, the more salubrious.)

I say “reorganized” – although Enigma will tell you they’ve “curated”-  the data, because the inspection outcomes have presumably been culled from New York’s remarkably near-real-time and far larger official data set, available on the city’s open data site (and Enigma’s too, though their version is three months old). The revision opens an interesting point of entry, then, to an understanding of how someone else’s data have been re-presented by someone else.

In what, then, does Enigma’s remake of the original data consist? For one thing, they’ve proposed to distill the source data set down to a unique entry for each restaurant (keep that that stratagem in mind), each of which, after all, have been subjected to several inspections.  By means of verification I aimed a Remove Duplicates check at the camis field comprising restaurant ids, and came away with but six redundancies – not too bad for a compendium of nearly 25,000 records.

And once having completed that chore we can run a simple but revealing pivot-tabled census of New York’s eateries by borough:

Rows: boro

Values: boro (count)

boro (again, by % of Column Total)

I get:

resto1

No one will be surprised by Manhattan’s restaurant plurality, though it should be added that the residential populations of both Brooklyn and Queens far exceed that of the storied island. In addition, keep in mind that the endless turnover of restaurants (the Quora article linked above declares an annual restaurant closure rate of 26%, though that assertion should probably be researched), turns the count into an implacably moving target.

And for another thing, the Engima set has padded the progenitor data with each restaurant’s geo-coordinates (latitude-longitude), thus priming a mapping capability. But they’ve also, befitting one of Enigma’s enigmatic apparent first principles, reformatted the inspection dates into text mode.

And Enigma’s alternate take has also put the scissors to some of the set’s original fields. The Critical Flag field – naming restaurants that incurred what the Department of Health and Hygiene terms critical violations, “…those most likely to contribute to food-borne illness”, is gone, and I’m not sure why. Those data sound like something you’d want to know about, and analyze.

But there’s a pointedly more serious issue besetting the data that I haven’t quite figured out. Because Engima determined to squeeze the data into a one-record-per-restaurant yield, it had to decide exactly which record would be earmarked for retention; and common analytical sense would commend the latest such record, conveying the current inspection standing for each restaurant. But it appears that Enigma hasn’t always nominated the latest record. A spot comparison of the records across the two datasets turned up some Enigma selections that predate more current inspections for the same restaurant in the official New York workbook. And if those kinds of discrepancies riddle the Enigma data, then we need to wonder about the decision rule that authorized their inclusion – and I don’t know what it is. What would an aggregate averaging of inspection scores purport to say, if some of the scores have been superseded by newer ones? (My emailed query to Enigma about the matter remains unanswered as of this writing.)

Moreover, because the one-record stipulation is in force, Enigma was impelled to collapse disparate violation codes in that eponymous field. The very first record, for example, for the Morris Park Bake Shop, reports two violations coded 10F and 8C, both filed on May 11, 2018. But New York’s precedent dataset has assigned a distinct record to each of the two, easing a pivot table breakout by code.

And those code consolidations – an ineluctable follow-on of the one-record-per-restaurant decision – probably explains Enigma’s omission in turn of the original Violation Description field. Boxing multiple violations in the space of one cell might confound legibility for both researchers and readers, and so Enigma likely concluded the whole field was best expurgated – at a price of course, because now we don’t know what the violation codes mean.

Now to be fair, Enigma also furnishes a worksheet-housed directory of those codes, which make for a most serviceable lookup array; but the multiple-code cell structure of its inspection data makes for an exceedingly messy prospect for 24,000-plus lookup values, which must be individuated somehow.

But all these cogitations have given me the munchies. Where do you want to eat? You want Chinese? Fine – that pares the choices to around 2,400. Your treat.

Walking Across the Brooklyn Bridge: Stepping Through the Data, Part 2

24 Dec

The decision to walk across the Brooklyn Bridge is a distinctly multivariate one, even if the internal equation that sets the walk in motion doesn’t chalk its terms on the walker’s psychic blackboard.

That preamble isn’t nearly as high-falutin’ as it sounds. Nearly all social activities negotiate trades-off between these and those alternatives, and a promenade over the bridge is no different. We’ve already observed the great, and expected, variation in bridge crossings by hour of the day in the previous post, and we could next consider the impact – if it’s proper to think about the matter in those causal terms – of month of the year on journey distribution (remember that our data records bridge crossings from October 1 2017 through July 31 of this year).

That objective calls for this straightforward pivot table:

Rows: hour_beginning (grouped by Year and Month. You need to put both of those grouping parameters in place in order to properly sequence the months, which straddle parts of two years.)

Values: Sum

Sum (again, here by % of Column Total)

I get:

bb1

The differentials are formidable, for me surprisingly so. One would have expected bridge foot traffic to crest in the summer, but a July-January walker ratio of 2.8 comes as a surprise, at least to me (remember again that the above totals compute one-way trips). It’s clear that meteorology has a lot to do with the decision to press ahead on the bridge, in addition to, or in conjunction with, chronology, i.e. the hour of day and day of the week. What we can’t know from the findings is whether the walkers had to get from Brooklyn to Manhattan or vice versa one way or another and chose to walk, or whether the trips were wholly discretionary.

And would one expect a spot of rain to discourage walkers? One suspects as much, of course, but confirmation or denial should be but a few clicks away. We could, for example, write a simple CORREL formula to associate precipitation with pedestrian turnout, provided we understand what it is we’re correlating. Here we need to remind ourselves that because we subjected in the previous post to a Get & Transform routine which replicated the pedestrian data source, that copy rolled twice as many rows we found in the orignal, assigning a record each to Towards Manhattan and Towards Brooklyn hourly totals. As a result each hourly precipitation figure is counted twice there, and so simplicity would have us look at rainfall data in the original dataset, if you still have it. If you do, this CORREL expression, which assesses precipitation by hour:

=CORREL(B2:B7297,H2:H7297)

Delivers a figure of -.0093, or a rather trifling fit between rain/snow and the determination to walk the bridge. Now that doesn’t look or sound right; but that perception is my way of saying it doesn’t comport with my commonsensical first guess.

But the correlation is “right”, in light of the manner in which I’ve framed the relationship. Because the formula considers precipitation with hourly pedestrian totals, most of the rainfall entries are overwhelmingly minute, and indeed, in over 4800 cases – almost two-thirds of all the hourly readings – amount to zero. The correlation appears to capitulate to what is, in effect, a host of unrelated walk/rainfall pairs.

But if you correlate walk numbers with aggregate rainfall by entire days the numbers read very differently. Continuing to the work with the original dataset, try this pivot table:

Rows: hour_beginning (grouped by Days)

Values: Pedestrians

Precipitation (both sum)

(Note that the row labels naturally nominate 1-Jan as the first entry, even as that date isn’t really the earliest. Remember the demonstration project got underway on October 1, 2017. But chronological order – really a lowest-to-highest numeric sort – is in no way a correlational necessity.)

Running a correlation on the above outcomes I get an association of -.333, which makes my common sense feel better about itself. That is, as calibrated here, rain “affects” pedestrian turnout to a fairly appreciable extent – the more rain, the fewer walkers, more or less. Again the (negative) correlation reflects the precipitation aggregated by days, not hours. Indeed – just 47 of the recorded 304 days report no precipitation at all.

And how does temperature figure in the decision to traverse the bridge? Again working with the original data set (and not the pivot table), in which each hourly instance appears once, we can rewrite the correlation, this time introducing the temperature field, which I have in the G column:

=CORREL(C2:C7297,G2:G7297)

I get .391, another persuasive, if partial relationship. With higher temperatures come stepped-up foot traffic – to a degree, pun intended – but that finding induces a couple of hesitations. For one thing, the Fahrenheit system to which the temperatures are here committed promotes an arbitrary, famous understanding, as it were – the temps aren’t keyed to an absolute zero. And so it occurred to me that a second correlation, this one redrawn with the temperatures pitched in Centigrade mode, crunch out a different result. That statistical hunch had me open a new temporary column (in my case in H), in which I refigured the temps with the cooperative CONVERT function, e.g.

=CONVERT(G2,”F”,”C”)

Copying down H and reprising the CORRELATION, this time with the C and H-columns range in tow, I wound up with… .391, at one with the first result, at least if you’re happy with a 3-decimal round-off, and I think I am.

But in fact the two .391s depart from one another by an infinitesimal sliver. The first, associating walk totals with temperatures expressed in Fahrenheit, comes to .390815536. That correlation with the temperatures in Centigrade (Celsius) calculates to .390959393. Presumably the tiny shift in numeric gravity wrought by the respective measurement systems accounts for the difference, about which few are likely to care, to be sure. But that discrepancy does mean I need to learn more about the workings of correlations.

The other caution about the correlation, whichever one chooses, asks about its linearity. While we could reasonably anticipate a swell in bridge crossings as the mercury ascends, it’s most possible, on the other hand, that pedestrian activity could be inhibited by temperatures forbiddingly high – in the 90s, for example.

And that conjecture could be submitted put to a pivot table (small note: two rows among the data record no temperatures), e g, assuming again we’ve remained with the original dataset, which features each temperature only once:

Rows: temperature (grouped, say, in bins of five degrees)

Values: Pedestrians (sum)

Pedestrians (count)

I get:

bb2

(The blanks reference the two empty temperature cells, and can be filtered out.)

The pedestrian count in effect totals the number of days populating each grouped temperature bin. After having filtered the blanks, move into the next-available D column – a space external to the pivot table – and enter in D4:

=B4/C4

Round to two decimal points and copy down D (I don’t think a calculated field can must this result). I get:

bb3

We’ve disclosed a strong if imperfect (and unsurprising) upward association between pedestrian hour averages and temperature. But the highest reading – 89-94 degrees – does seem to drive a pull-back in traffic. Note in addition the leap in hourly crossings from the 74-78 to 79-83 bins, as if 80 degrees or so lifts the inclination to walk to its tipping point.

So there. Didn’t I tell you the decision to lace up those high-heeled sneakers was multivariate?

P.S. In response to my previous post’s curiosity about a few missing Towards Brooklyn/Manhattan data, New York’s Department of Transportation wrote me that the empty entries might be attributable to a weather-induced snarl.