[FEA] DataFrame pct_change

[beckernick]

Series.pct_change was implemented in cuDF Python in #8650 . For pandas compatibility, it would be nice to implement this for DataFrames. The DataFrame method calculates the percent change individually for each column.

As a starting point, it would make sense to limit the supported parameters/configuration currently supported by Series.pct_change.

import pandas as pd
​
df = pd.DataFrame({
    'FR': [4.0405, 4.0963, 4.3149],
    'GR': [1.7246, 1.7482, 1.8519],
    'IT': [804.74, 810.01, 860.13]},
    index=['1980-01-01', '1980-02-01', '1980-03-01'])
​
print(df, "\n")
print(df.pct_change())
                FR      GR      IT
1980-01-01  4.0405  1.7246  804.74
1980-02-01  4.0963  1.7482  810.01
1980-03-01  4.3149  1.8519  860.13 

                  FR        GR        IT
1980-01-01       NaN       NaN       NaN
1980-02-01  0.013810  0.013684  0.006549
1980-03-01  0.053365  0.059318  0.061876