Timestamp index for pandas dataframe from read_json()

Question

I'm reading a single JSON line from file data.json with this content:

[
  {
    "timestamp": 1436266865,
    "rates": {
      "EUR": 0.911228,
      "JPY": 122.5463,
      "AUD": 1.346118
    }
  },
  {
    "timestamp": 1436277661,
    "rates": {
      "JPY": 122.4789,
      "AUD": 1.348871,
      "EUR": 0.91433
    }
  }
]

into a pandas DataFrame. I want to use the "timestamp" as the DataFrame's index. I achieve this by:

df = pandas.read_json('data.json')
df.index = df['timestamp']
df.drop('timestamp', axis=1, inplace=1)

Is it possible to do it in just one line?

Leb · Accepted Answer · 2015-09-30 13:20:19Z

11

import pandas as pd

df = pd.read_json('data.json')
df.set_index('timestamp',inplace=True)
print(df)

What this will do is set timestamp to your index. inplace=True will prevent you having to do df=df.set_index('timestamp') and by default it'll drop the column.

                                                        rates
timestamp                                                    
1436266865  {'EUR': 0.9112279999999999, 'JPY': 122.5463, '...
1436277661  {'JPY': 122.4789, 'AUD': 1.348871, 'EUR': 0.91...

answered Sep 30, 2015 at 13:20

Leb

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3 Comments

Leb Over a year ago

What one-line are you referring to?

latgarf Over a year ago

Why this one-liner wouldn't work? df = pd.read_json('data.json').set_index('timestamp', inplace=True)

Leb Over a year ago

Because the dataframe has not been set yet, so you can't call .set_index on it unless it has been executed in memory. The code is being done from left to right after it's been read from right to left. So calling on .set_index for an undefined DF will result in None. Does that clarify things?

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