So I haven’t been as good at blogging for the past month. My last post was on week 3 at RC, yikes. In the meantime, I have:

And most recently poked around some MTA Subway data.

Doing stuff with the MTA data

For the uninitiated, the Metropolitan Transit authority, MTA runs the subway and buses in NYC. And they have an API. Whattt.

Turnstile data!

I didn’t play with the API though. I was more interested in their Turnstile data which has weekly logs of cumulative entries and exits per turnstile per subway station at some time interval.

Which means, perfect for subway traffic analysis. Only that the data was in 200,000 line long, 20MB txt files in two different formats. For one week’s worth of numbers. Nnnnggghhh.

Scraping, parsing, cleaning with SQL!

I spent quite a bit of time writing code to parse the data and to dump it into a database. Let me just say that the data was not at all pretty. Logging intervals vary by stations and happen and different times of the day. The turnstile counters also get reset every now and then on different days.

I wrote a handy command line tool to scrape MTA data so you can specify a date range and it will grab the files from that range and dump the raw data in a db. You can find it on Github here and a sample dataset for Sept 2015 here:

Scraper Sept 2015 data

I also wrote a script to clean the data and do some simple cleaning. More details on the README:

Data cleaner

Because of all the wonky different formatting, writing simple tests to make sure that my code was working turned out to pay dividends, especially when I started adding edge cases and working with new things like SQLite. This was also my first time writing SQL queries and learning things like:

  • how to select and group stuff!
  • queries are hella slow because it’s reading from disk and should be minimized
  • learning how to think in tables. grouping data and working with those chunks speeds things up a lot.

Thinking in tables

I talked to from Jesse, an RC alum who was super helpful with thinking about the data. The main thing I was trying to do was to find the number of entries/exits for a particular timeframe (which wasn’t explicit because MTA only gives you the running cumulative numbers at every entry).

Instead of having to look through the entire database for the previous entry to find the difference (which took way too long, about an hour with 200,000 rows), he suggested grouping the data by unique turnstile (about 4000+ of them), sorting by date, then lookup for the previous entry would just be the one before, i.e. O(1). In total that would only be 1 query to get list of unique turnstiles, followed by 4000+ queries for each turnstile, which turned out to be waaay faster (under 5 minutes).

Also, working with Python has been a pleasure, especially when it comes to writing simple assert tests, something I haven’t been able to make into a habit with Javascript.

I have useful data, now what?

Now that we have cleaner data, we can do stuff with it! Some preliminary data.

Note: Take it with a grain of salt because I haven’t checked for outliers

Edit: turns out I was working on the wrong database with cumulative entries instead when I queried this (facepalm). Have fixed with data from the right database this time around. Still a little wonky, will have to learn how to filter out outliers later.

Edit 2: also turns out I have a lot of outliers. Did a simple pruning by standard deviation and ended up with this data. Still had to remove a couple of clear outliers by hand, but data makes sense now!

Note the repetition in 42 ST station names – I’m not sure how or why this is, so ideas are welcome.

I’m assuming that 42 ST-PA BUS TE is the one that runs on the ACE line and 42 ST-TIMES SQ is on the 123 line. The subsequent lines are just lines that they are connected to?

----------  ----------  ------------  ----------  -------------
728605      R170        14 ST-UNION   456LNQR     2675454      
733260      R046        42 ST-GRD CN  4567S       1789939      
679390      R022        34 ST-HERALD  BDFMNQR     1732995      
714660      R084        59 ST-COLUMB  1ABCD       1729229      
713284      R033        42 ST-TIMES   1237ACENQR  1584018      
637233      R012        34 ST-PENN S  ACE         1563049      
738398      R179        86 ST         456         1562741      
765251      R055        MAIN ST       7           1525426      
711512      R293        34 ST-PENN S  123ACE      1356457      
635141      R011        42 ST-PA BUS  ACENQRS123  1342426 

All stations on the G line in descending popularity

Yes, I take the G a lot, and kind of like how small and unpopular it is! Look at the ridership difference between METROPOLITAN AV and 42 ST above. Seems like there are a lot of people who live in LIC/Astoria that take the G all the way up. I’m surprised that HOYT doesn’t rank higher because it transfers to the ACE, but then again, most people would have gone on elsewhere and transferred without going through the turnstiles. We’re losing out on a lot of transfer data here.

----------  ---------------  ----------  -------------  -----------
R268        METROPOLITAN AV  GL          406604         204217     
R359        COURT SQ         EMG         393372         206356     
R258        4 AVE            DFGMNR      317127         285127     
R288        7 AV-PARK SLOPE  FG          272005         60317      
R204        CHURCH AVE       FG          270687         169046     
R129        BERGEN ST        FG          270588         166326     
R220        CARROLL ST       FG          268265         121279     
R217        HOYT/SCHERMER    ACG         240597         213857     
R256        NASSAU AV        G           218548         113352     
R239        GREENPOINT AVE   G           218107         155785     
R269        BEDFORD/NOSTRAN  G           198039         110727     
R241        15 ST-PROSPECT   FG          146397         63455      
R286        MYRTLE-WILLOUGH  G           144565         79652      
R289        FT HAMILTON PKY  FG          134171         38559      
R317        CLINTON-WASH AV  G           132916         19985      
R270        SMITH-9 ST       FG          126743         142212     
R287        CLASSON AVE      G           122914         116782     
R318        FULTON ST        G           114912         110825     
R299        BROADWAY         G           102202         85013      
R316        FLUSHING AVE     G           64595          64798      
R360        VAN ALSTON-21ST  G           45890          50158 

I also have other snippets of data on the Github README.

What’s next

Gonna work on extracting more interesting data and a visualizer!

If you like trains, check out fun facts from the MTA and a previously created turnstile visualizer.

Also, missing the Summer 2s already, but on the flipside we had a huge new batch of Fall 2 RCers join us this Monday! It’s already past the halfway point of RC and time feels like it’s running out too fast.

Back to code!

*From dates of 2015-08-29 to 2015-09-25