CODEWITHSUNDEEP
pandas
user3222101
user3222101

Reputation: 1330

How to subtract value from same month last year in pandas?

I have the below dataframe and I need to subtract value from same month last year and save it in output:

date            value     output
01-01-2012      20        null
01-02-2012      10
01-03-2012      40
01-06-2012      30
01-01-2013      20           0
01-02-2013      30          20
01-02-2014      60          30
01-03-2014      50          null

Upvotes: 1

Views: 498

Answers (1)

jezrael
jezrael

Reputation: 862481

First create DatetimeIndex, then subtract by sub with new Series by shift by 12 months, MS is for start of month:

df['date'] = pd.to_datetime(df['date'], dayfirst=True)
df = df.set_index('date')

df['new'] = df['value'].sub(df['value'].shift(freq='12MS'))
print (df)
            value  output   new
date                           
2012-01-01     20     NaN   NaN
2012-02-01     10     NaN   NaN
2012-03-01     40     NaN   NaN
2012-06-01     30     NaN   NaN
2013-01-01     20     0.0   0.0
2013-02-01     30    20.0  20.0
2014-02-01     60    30.0  30.0
2014-03-01     50     NaN   NaN

Upvotes: 2

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