How to show last occurence of a certain value in a Pandas column?-CodePudding

Let's say I have this DataFrame

     time  status
0   10:00      On
1   10:01     Off
2   10:02     Off
3   10:03     Off
4   10:04      On
5   10:05     Off
6   10:06     Off
7   10:07     Off
8   10:08     Off
9   10:09      On
10  10:10     Off

I want to add a column that shows the previous time the status was "on", as follows

     time  status  last_on
0   10:00      On      NaN
1   10:01     Off    10:00
2   10:02     Off    10:00
3   10:03     Off    10:00
4   10:04      On    10:00
5   10:05     Off    10:04
6   10:06     Off    10:04
7   10:07     Off    10:04
8   10:08     Off    10:04
9   10:09      On    10:04
10  10:10     Off    10:09

Any thoughts?

CodePudding user response：

you could try something like this:

df['last_on']= df.time.where(df.status=='On').shift().ffill()