Python 实用宝典

Question 1

What I am trying to do is extract elevation data from a google maps API along a path specified by latitude and longitude coordinates as follows:

from urllib2 import Request, urlopen
import json

path1 = '42.974049,-81.205203|42.974298,-81.195755'
request=Request('http://maps.googleapis.com/maps/api/elevation/json?locations='+path1+'&sensor=false')
response = urlopen(request)
elevations = response.read()

This gives me a data that looks like this:

elevations.splitlines()

['{',
 '   "results" : [',
 '      {',
 '         "elevation" : 243.3462677001953,',
 '         "location" : {',
 '            "lat" : 42.974049,',
 '            "lng" : -81.205203',
 '         },',
 '         "resolution" : 19.08790397644043',
 '      },',
 '      {',
 '         "elevation" : 244.1318664550781,',
 '         "location" : {',
 '            "lat" : 42.974298,',
 '            "lng" : -81.19575500000001',
 '         },',
 '         "resolution" : 19.08790397644043',
 '      }',
 '   ],',
 '   "status" : "OK"',
 '}']

when putting into as DataFrame here is what I get:

pd.read_json(elevations)

and here is what I want:

I’m not sure if this is possible, but mainly what I am looking for is a way to be able to put the elevation, latitude and longitude data together in a pandas dataframe (doesn’t have to have fancy mutiline headers).

If any one can help or give some advice on working with this data that would be great! If you can’t tell I haven’t worked much with json data before…

EDIT:

This method isn’t all that attractive but seems to work:

data = json.loads(elevations)
lat,lng,el = [],[],[]
for result in data['results']:
    lat.append(result[u'location'][u'lat'])
    lng.append(result[u'location'][u'lng'])
    el.append(result[u'elevation'])
df = pd.DataFrame([lat,lng,el]).T

ends up dataframe having columns latitude, longitude, elevation

Question 2

I found a quick and easy solution to what I wanted using json_normalize() included in pandas 1.01.

from urllib2 import Request, urlopen
import json

import pandas as pd    

path1 = '42.974049,-81.205203|42.974298,-81.195755'
request=Request('http://maps.googleapis.com/maps/api/elevation/json?locations='+path1+'&sensor=false')
response = urlopen(request)
elevations = response.read()
data = json.loads(elevations)
df = pd.json_normalize(data['results'])

This gives a nice flattened dataframe with the json data that I got from the Google Maps API.

Question 3

Check this snip out.

# reading the JSON data using json.load()
file = 'data.json'
with open(file) as train_file:
    dict_train = json.load(train_file)

# converting json dataset from dictionary to dataframe
train = pd.DataFrame.from_dict(dict_train, orient='index')
train.reset_index(level=0, inplace=True)

Hope it helps :)

Question 4

You could first import your json data in a Python dictionnary :

data = json.loads(elevations)

Then modify data on the fly :

for result in data['results']:
    result[u'lat']=result[u'location'][u'lat']
    result[u'lng']=result[u'location'][u'lng']
    del result[u'location']

Rebuild json string :

elevations = json.dumps(data)

Finally :

pd.read_json(elevations)

You can, also, probably avoid to dump data back to a string, I assume Panda can directly create a DataFrame from a dictionnary (I haven’t used it since a long time :p)

Question 5

Just a new version of the accepted answer, as python3.x does not support urllib2

from requests import request
import json
from pandas.io.json import json_normalize

path1 = '42.974049,-81.205203|42.974298,-81.195755'
response=request(url='http://maps.googleapis.com/maps/api/elevation/json?locations='+path1+'&sensor=false', method='get')
elevations = response.json()
elevations
data = json.loads(elevations)
json_normalize(data['results'])

Question 6

The problem is that you have several columns in the data frame that contain dicts with smaller dicts inside them. Useful Json is often heavily nested. I have been writing small functions that pull the info I want out into a new column. That way I have it in the format that I want to use.

for row in range(len(data)):
    #First I load the dict (one at a time)
    n = data.loc[row,'dict_column']
    #Now I make a new column that pulls out the data that I want.
    data.loc[row,'new_column'] = n.get('key')

Question 7

Optimization of the accepted answer:

The accepted answer has some functioning problems, so I want to share my code that does not rely on urllib2:

import requests
from pandas import json_normalize
url = 'https://www.energidataservice.dk/proxy/api/datastore_search?resource_id=nordpoolmarket&limit=5'

response = requests.get(url)
dictr = response.json()
recs = dictr['result']['records']
df = json_normalize(recs)
print(df)

Output:

        _id                    HourUTC               HourDK  ... ElbasAveragePriceEUR  ElbasMaxPriceEUR  ElbasMinPriceEUR
0    264028  2019-01-01T00:00:00+00:00  2019-01-01T01:00:00  ...                  NaN               NaN               NaN
1    138428  2017-09-03T15:00:00+00:00  2017-09-03T17:00:00  ...                33.28              33.4              32.0
2    138429  2017-09-03T16:00:00+00:00  2017-09-03T18:00:00  ...                35.20              35.7              34.9
3    138430  2017-09-03T17:00:00+00:00  2017-09-03T19:00:00  ...                37.50              37.8              37.3
4    138431  2017-09-03T18:00:00+00:00  2017-09-03T20:00:00  ...                39.65              42.9              35.3
..      ...                        ...                  ...  ...                  ...               ...               ...
995  139290  2017-10-09T13:00:00+00:00  2017-10-09T15:00:00  ...                38.40              38.4              38.4
996  139291  2017-10-09T14:00:00+00:00  2017-10-09T16:00:00  ...                41.90              44.3              33.9
997  139292  2017-10-09T15:00:00+00:00  2017-10-09T17:00:00  ...                46.26              49.5              41.4
998  139293  2017-10-09T16:00:00+00:00  2017-10-09T18:00:00  ...                56.22              58.5              49.1
999  139294  2017-10-09T17:00:00+00:00  2017-10-09T19:00:00  ...                56.71              65.4              42.2

PS: API is for Danish electricity prices

Question 8

Here is small utility class that converts JSON to DataFrame and back: Hope you find this helpful.

# -*- coding: utf-8 -*-
from pandas.io.json import json_normalize

class DFConverter:

    #Converts the input JSON to a DataFrame
    def convertToDF(self,dfJSON):
        return(json_normalize(dfJSON))

    #Converts the input DataFrame to JSON 
    def convertToJSON(self, df):
        resultJSON = df.to_json(orient='records')
        return(resultJSON)

Question 9

billmanH’s solution helped me but didn’t work until i switched from:

n = data.loc[row,'json_column']

to:

n = data.iloc[[row]]['json_column']

here’s the rest of it, converting to a dictionary is helpful for working with json data.

import json

for row in range(len(data)):
    n = data.iloc[[row]]['json_column'].item()
    jsonDict = json.loads(n)
    if ('mykey' in jsonDict):
        display(jsonDict['mykey'])

Question 10

#Use the small trick to make the data json interpret-able
#Since your data is not directly interpreted by json.loads()

>>> import json
>>> f=open("sampledata.txt","r+")
>>> data = f.read()
>>> for x in data.split("\n"):
...     strlist = "["+x+"]"
...     datalist=json.loads(strlist)
...     for y in datalist:
...             print(type(y))
...             print(y)
...
...
<type 'dict'>
{u'0': [[10.8, 36.0], {u'10': 0, u'1': 0, u'0': 0, u'3': 0, u'2': 0, u'5': 0, u'4': 0, u'7': 0, u'6': 0, u'9': 0, u'8': 0}]}
<type 'dict'>
{u'1': [[10.8, 36.1], {u'10': 0, u'1': 0, u'0': 0, u'3': 0, u'2': 0, u'5': 0, u'4': 0, u'7': 0, u'6': 0, u'9': 0, u'8': 0}]}
<type 'dict'>
{u'2': [[10.8, 36.2], {u'10': 0, u'1': 0, u'0': 0, u'3': 0, u'2': 0, u'5': 0, u'4': 0, u'7': 0, u'6': 0, u'9': 0, u'8': 0}]}
<type 'dict'>
{u'3': [[10.8, 36.300000000000004], {u'10': 0, u'1': 0, u'0': 0, u'3': 0, u'2': 0, u'5': 0, u'4': 0, u'7': 0, u'6': 0, u'9': 0, u'8': 0}]}
<type 'dict'>
{u'4': [[10.8, 36.4], {u'10': 0, u'1': 0, u'0': 0, u'3': 0, u'2': 0, u'5': 0, u'4': 0, u'7': 0, u'6': 0, u'9': 0, u'8': 0}]}
<type 'dict'>
{u'5': [[10.8, 36.5], {u'10': 0, u'1': 0, u'0': 0, u'3': 0, u'2': 0, u'5': 0, u'4': 0, u'7': 0, u'6': 0, u'9': 0, u'8': 0}]}
<type 'dict'>
{u'6': [[10.8, 36.6], {u'10': 0, u'1': 0, u'0': 0, u'3': 0, u'2': 0, u'5': 0, u'4': 0, u'7': 0, u'6': 0, u'9': 0, u'8': 0}]}
<type 'dict'>
{u'7': [[10.8, 36.7], {u'10': 0, u'1': 0, u'0': 0, u'3': 0, u'2': 0, u'5': 0, u'4': 0, u'7': 0, u'6': 0, u'9': 0, u'8': 0}]}
<type 'dict'>
{u'8': [[10.8, 36.800000000000004], {u'1': 0, u'0': 0, u'3': 0, u'2': 0, u'5': 0, u'4': 0, u'7': 0, u'6': 0, u'9': 0, u'8': 0}]}
<type 'dict'>
{u'9': [[10.8, 36.9], {u'1': 0, u'0': 0, u'3': 0, u'2': 0, u'5': 0, u'4': 0, u'7': 0, u'6': 0, u'9': 0, u'8': 0}]}

Question 11

Once you have the flattened DataFrame obtained by the accepted answer, you can make the columns a MultiIndex (“fancy multiline header”) like this:

df.columns = pd.MultiIndex.from_tuples([tuple(c.split('.')) for c in df.columns])

Python 实用宝典

JSON转换为Pandas DataFrame

问题：JSON转换为Pandas DataFrame

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