load_walking_data.py

import json
import pandas as pd
import matplotlib.pyplot as plt

import synapseclient
from collections import OrderedDict

syn = synapseclient.Synapse()
syn.login()

results = syn.tableQuery('SELECT count(*) FROM syn5299184')
print "Total number of records:", results.asInteger()

## Get a limited number of records
results = syn.tableQuery('SELECT * FROM syn5299184 LIMIT 20')
file_map = syn.downloadTableColumns(results, ["deviceMotion_walking_outbound.json.items"])

## if we download all the data, we'll see that one is missing. This shows us why:
results = syn.tableQuery('SELECT * FROM syn5299184 where "deviceMotion_walking_outbound.json.items" IS NULL')
for result in results:
    print result

## load the json files
data = OrderedDict()
for file_handle, path in file_map.iteritems():
    with open(path) as f:
        data[file_handle] = json.loads(f.read())

## Each json file is a list of maps whose keys are:
##  * userAcceleration
##  * timestamp
##  * magneticField
##  * gravity
##  * rotationRate
##  * attitude

## data[data.keys()[0]][0].keys()

## Here are the data types
names = ['attitude',
         'userAcceleration',
         'rotationRate',
         'gravity',
         'magneticField']

## build dataframes for all data types except timestamp, which
## becomes the index for the others.
records = OrderedDict()
for file_handle, rs in data.iteritems():
    series = OrderedDict()
    timestamps = [r['timestamp'] for r in rs]
    t0 = min(timestamps)
    timestamps = [t-t0 for t in timestamps]
    for name in names:
        series[name] = pd.DataFrame([r[name] for r in rs], index=timestamps)
    records[file_handle] = series

## graph the gravity data type for one record
g = records[records.keys()[0]]['gravity']
plt.plot(g.index, g.x, 'r', g.index, g.y, 'g', g.index, g.z, 'b')
plt.show()

## graph the gravity data type for a sequence of records
for i,key in enumerate(records.keys()):
    g = records[key]['gravity']
    plt.plot(g.index, g.x, 'r', g.index, g.y, 'g', g.index, g.z, 'b')
    plt.show()
    if i > 10: break