Change column value based on conditions in other columns in Pandas

Question

I want to change the value in 1 column in the data frame based on the conditions and comparison of values in other columns.

This is the original data frame:

        start         end diff
0  2016-05-08     unknown  3
1  2016-05-08  2017-09-08  5
2  2018-09-01  2017-09-01  5

This is the data frame that I want:

        start         end diff
0  2016-05-08     unknown  3
1  2016-05-08  2017-09-08  1
2  2018-09-01  2017-09-01  -1

Basically, I want the values in diff column to remain the same if end is unknown, otherwise, I want it to be the value of year value of end - year value of start.

Can anyone suggest a piece of code?

Thanks in advance!

BENY · Accepted Answer · 2019-07-23 21:23:40Z

1

Here is one way using np.where , after convert the datatime by using to_datetime. Also , please do not name a columns with build-in function name like : diff, sum , min, max and cumsum.

df.start=pd.to_datetime(df.start)
df.end=pd.to_datetime(df.end,errors = 'coerce')
df['diff']=np.where(df.end.isnull(),df['diff'],df.end.dt.year-df.start.dt.year)
df
Out[135]: 
       start        end  diff
0 2016-05-08        NaT   3.0
1 2016-05-08 2017-09-08   1.0
2 2018-09-01 2017-09-01  -1.0

answered Jul 23, 2019 at 21:23

BENY

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