How can I advance the index of a pandas.dataframe by one quarter?

Question

I would like to shift the index of a pandas.dataframe by one quarter. The dataframe looks like:

            ID   Nowcast  Forecast
1991-01-01   35   4144.70   4137.40
1991-01-01   40   4114.00   4105.00
1991-01-01   60   4135.00   4130.00
....

So far, I calculate the number of occurrences of the first timestamp 1991-01-01 and shifted the dataframe accordingly. The code is:

Stamps = df.index.unique()
zero = 0
for val in df.index:
    if val == Stamps[0]:
        zero = zero + 1
df = df.shift(zero)

The operation results in the following dataframe:

              ID   Nowcast  Forecast 
1991-04-01   35.0   4144.70   4137.40       
1991-04-01   40.0   4114.00   4105.00       
1991-04-01   60.0   4135.00   4130.00  

The way I'm doing this strikes me as inefficient and error-prone. Is there a better way?

Answer 1

you can use pd.DateOffset() :

In [110]: df
Out[110]:
            ID  Nowcast  Forecast
1991-01-01  35   4144.7    4137.4
1991-01-01  40   4114.0    4105.0
1991-01-01  60   4135.0    4130.0

In [111]: df.index += pd.DateOffset(months=3)

In [112]: df
Out[112]:
            ID  Nowcast  Forecast
1991-04-01  35   4144.7    4137.4
1991-04-01  40   4114.0    4105.0
1991-04-01  60   4135.0    4130.0