Python2.7: Change Difference For A Column Value Of Dataframe

I have a dataframe(df) like as following(just example), there are maybe 10 or more dataframes: date a b 0 2010-01-01 12 15 1 2010-01-02

Solution 1:

You can use pct_change, but first divide value of b by condition:

dates = ['2010-01-09','2011-01-09']
m = df2['date'].isin(dates)
df2.loc[m, 'b'] =  df2['b'] / 10

df2['b_diff'] = df2['b'].pct_change()
print (df2)
        date    a     b    b_diff
0 2010-01-01   12  15.0       NaN
1 2010-01-02   13  20.0  0.333333
2 2010-01-03   14  23.0  0.150000
3 2010-01-04   15  24.0  0.043478
4 2010-01-05   16  25.0  0.041667
5 2010-01-08   17  15.0 -0.400000
6 2010-01-09  180  16.0  0.066667

Alternative solution:

dates = ['2010-01-09','2011-01-09']
m = df2['date'].isin(dates)

df2['b'] = df2['b'].mask(m, df2['b'] / 10)
df2['b_diff'] = df2['b'].pct_change()
print (df2)
        date    a     b    b_diff
0 2010-01-01   12  15.0       NaN
1 2010-01-02   13  20.0  0.333333
2 2010-01-03   14  23.0  0.150000
3 2010-01-04   15  24.0  0.043478
4 2010-01-05   16  25.0  0.041667
5 2010-01-08   17  15.0 -0.400000
6 2010-01-09  180  16.0  0.066667