CODEWITHSUNDEEP
pandas
Stacey
Stacey

Reputation: 5097

Finding the min values in a data frame column for each day

I have a dataframe (df) that looks like:

            Value
03/03/2014      3
03/03/2014      3
03/03/2014      6
03/03/2014      4
03/03/2014      5
03/03/2014      3
03/03/2014      5
03/03/2014      8
03/03/2014      7
04/03/2014      6
04/03/2014      9
04/03/2014      2
04/03/2014      3
04/03/2014     10
04/03/2014      6
04/03/2014      7
04/03/2014      5
04/03/2014      7
05/03/2014      1
05/03/2014      9
05/03/2014      5
05/03/2014      9
05/03/2014      2
05/03/2014      9
05/03/2014      6
05/03/2014      8
05/03/2014      1
06/03/2014      9
06/03/2014     10
06/03/2014      9
06/03/2014      6
06/03/2014      8
06/03/2014      5
06/03/2014     10
06/03/2014      5
06/03/2014     10
07/03/2014      8
07/03/2014      7
07/03/2014      4
07/03/2014      5
07/03/2014      9
07/03/2014      2
07/03/2014      3
07/03/2014      2
07/03/2014      4

I would like to add a new column DayMin which contains the minimum value for each day in column Value and would look like:

            Value   DayMin
03/03/2014      3        3
03/03/2014      3        3
03/03/2014      6        3
03/03/2014      4        3
03/03/2014      5        3
03/03/2014      3        3
03/03/2014      5        3
03/03/2014      8        3
03/03/2014      7        2
04/03/2014      6        2
04/03/2014      9        2
04/03/2014      2        2
04/03/2014      3        2
04/03/2014     10        2
04/03/2014      6        2
04/03/2014      7        2
04/03/2014      5        2
04/03/2014      7        2
05/03/2014      1        1
05/03/2014      9        1
05/03/2014      5        1
05/03/2014      9        1
05/03/2014      2        1
05/03/2014      9        1
05/03/2014      6        1
05/03/2014      8        1
05/03/2014      1        1
06/03/2014      9        5
06/03/2014     10        5
06/03/2014      9        5
06/03/2014      6        5
06/03/2014      8        5
06/03/2014      5        5
06/03/2014     10        5
06/03/2014      5        5
06/03/2014     10        5
07/03/2014      8        2
07/03/2014      7        2
07/03/2014      4        2
07/03/2014      5        2
07/03/2014      9        2
07/03/2014      2        2
07/03/2014      3        2
07/03/2014      2        2
07/03/2014      4        2

I can see I can use df['DayMin']= df['Value'].min() to get the column global minimum. But I can't see how to do this for each day and return it to the df.

Upvotes: 1

Views: 32

Answers (1)

Quang Hoang
Quang Hoang

Reputation: 150735

You can use groupby().transform:

df['DayMin'] = df.groupby(level=0)['Value'].transform('min')

Upvotes: 3

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