CODEWITHSUNDEEP
pythonpandasdatecompare
Yakov Kemer
Yakov Kemer

Reputation: 373

Pandas compare values by dates

I have a data like

Date, Name, Something
2020-04-01,John,10
2020-04-01,Ivory,5
2020-04-01,Sam,3
2020-04-02,John,5
2020-04-02,Ivory,2
2020-04-02,Sam,1
2020-04-02,John,20
2020-04-02,Ivory,3
2020-04-02,Sam,9

working with pandas, i want to compare yesterday value by name, with today result to get the increase, decrease. shift(3) won't work because number of names are different for each day. How can i do it. I want to add previous number. I tried 

df['old_data'] = df[(work['Name'] == df['Name']) & (df['Date'] ==
                                                                 (df['Date'] - pd.Timedelta(days = 1))
                                                                 )]['Something']

but it didn't work.

Upvotes: 0

Views: 352

Answers (1)

dkritz
dkritz

Reputation: 354

Try this:

import pandas as pd


df = pd.DataFrame({'Date': {0:'2020-04-01', 1:'2020-04-01', 2:'2020-04-01', 
                             3:'2020-04-02', 4:'2020-04-02', 5:'2020-04-02', 
                             6:'2020-04-03', 7:'2020-04-03', 8:'2020-04-03'},
                    'Name': {0:'John', 1:'Ivory', 2:'Sam', 
                             3:'John', 4:'Ivory', 5:'Sam', 
                             6:'John', 7:'Ivory', 8:'Sam'},
                    'Something': {0:10, 1:5, 2:3, 
                                  3:5, 4:2, 5:1, 
                                  6:20, 7:3, 8:9}})

df['diff'] = df.groupby('Name')['Something'].diff()

df.dropna()

I changed your data by altering the last three dates to be '2020-04-03'.

Upvotes: 2

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