Parsing JSON Data from the Nextbike Platform
Given a semi-public API, what data analysis can we perform? The nextbike platform provides both an XML and JSON output of raw data, detailing bike availability at each station in the cities and countries where the system exists. In particular, we have used the JSON output to focus on Belfast (city 238) where BelfastBikes has 46 docking stations available to rent a bike from, although we can modify this to be any city on the platform, using the respective city number.
Using kdb+ we can pull this data periodically off the web and create a time-series database to perform analysis on, made possible by the TorQ framework. Taking advantage of TorQ's capabilities, the process has been enhanced to include error logging, history logging and an extension of the kdb+ built-in timer, making it repeat until a specified end-time. This allows us to view log files for any date and rebuild the usage of BelfastBikes for any date where we have collected information.
Once a database has been created, time-series and other queries can be executed against the data. For example, by rebuilding the table for yesterday's bike usage, we can create a mapping of 'routes' that each bike has taken, i.e. where the bike has checked in during those 24 hours and at what time during the day.
Basic knowledge of the q programming language and linux commands is assumed. This project requires the use of KDB+ and the TorQ framework.
- These bash commands will give directions on downloading TorQ and our BIKE message package. The BIKE package will be placed on top of the base TorQ package.
Make a directory to check the git repos into, and a directory to deploy the system to.
~/$ mkdir git deploy ~/$ ls deploy git
Change to the git directory and clone the BIKE parser and TorQ repositories.
~/$ cd git ~/git$ git clone https://github.com/AquaQAnalytics/TorQ-Bikes.git ~/git$ git clone https://github.com/AquaQAnalytics/TorQ.git ~/git$ ls TorQ-Bikes TorQ
Change to the deploy directory and copy the contents of TorQ into it.
~/git$ cd ../deploy/ ~/deploy$ cp -r ../git/TorQ/* ./
Copy the contents of the BIKE parsers repo into the same directory, allowing overwrites.
~/deploy$ cp -r ../git/TorQ-Bikes/* ./
You should have a combination of each directories content included in the deploy directory:
~/deploy$ ls appconfig aquaq-torq-brochure.pdf code config docs hdb html lib LICENSE logs mkdocs.yml README.md setenv.sh start_bikes.sh stop_bikes.sh tests torq.q jsonlogs
You can change the city that you want to collect data for by changing the city
number variable in
deploy/setenv.sh; the default value is 238 (Belfast).
The default port is set at 14000, this can also be modified in the
Launching the Process
To launch the process of retrieving data about each BelfastBikes location, run
start_bikes.sh executable in the
This launches the bikes.q script wrapped in the TorQ framework.
The process will run for 14 days once it starts, collecting data every 30 seconds. During the 14 days, there will be a write down to hdb at 6am every day using the previous day's data and saved by date. Within the bikes.q script there are timer functions for both the collection of data and the writedown which can be modified.
The jsonlogs directory will contain previously collected data in its raw JSON format for each day, saved as a plain text file.
In order to replay a log file on disk, the following can be used:
This reads the data to the in memory table
place, which can then be written to
To query the persisted data in the HDB, we can either load in a specific date partition to a q session, or load the entire database to perform queries across a range of dates. To load in the HDB to a q session we can run the following command:
~/deploy$ q hdb/
//For each bike, select the first time it appears at a distinct location (uid) s:1_select uid,time by bike_numbers from select from (update a:differ uid by bike_numbers from ungroup select time,uid,bike_numbers from place where date=2017.09.22) where a=1 //Create a table showing each uid and its corresponding location name, latitude and longitude, keyed by uid t:`uid xkey select name,lat,lng by distinct uid from place where date=2017.09.22 //Join together news and t, select relevant information grouped by bike numbers data:select uid,name,lat,lng,time by bike_numbers from lj[ungroup s;t]
This data table table will show what stations a particular bike has visited during that day.
Within a partition of our database, we could find out how many rentals were taken from each docking station during that particular day:
q)`x xdesc (select count i by uid from d:select from (update d: differ uid by bike_numbers from (ungroup select time,uid,bike_numbers from place)) where d,not bike_numbers=0) lj select last name by uid from place uid | x name -------| ---------------------------------------------- 316463 | 127 "Donegall Quay" 263966 | 101 "City Hall" 566097 | 43 "Titanic Belfast Met" 318535 | 23 "Odyssey / Sydenham Road" 517255 | 23 "Queens University / University Road " 318553 | 21 "Arthur Street / Chichester Street" 1257794| 19 "Belfast City Hospital Lisburn Rd" 555520 | 17 "Queens University / Botanic Gardens "
Or we could query across a range of dates within the database, for example finding out which docking station was most popular across several days:
q)select max x,Dock:name where x=max x by date from ((select count i by uid,date from d:select from (update d: differ uid by bike_numbers from (ungroup select date,time, uid,bike_numbers from place)) where d,not bike_numbers=0) lj select last name by uid from place) date | x Dock ----------| ----------------------------------------- 2017.09.23| 153 "Titanic Belfast Met" 2017.09.24| 127 "Donegall Quay" 2017.09.25| 41 "Alfred Street / St Malachy's Church"
Stopping the Process
In order to stop the process, run the
stop_bikes.sh executable, in the
This will save down data collected during the day and kill the process.