python - Pandas: change values in group to minimum -


what have:

df = pd.dataframe({'series1':['a','a','a','a','a','a','b','b','b','b','b','b','b','b','c','c','c','c','c'],                    'series2':[1,1,1,1,2,2,1,1,1,1,1,1,1,1,1,1,1,1,1],                    'series3':[10,12,20,10,12,4,8,8,1,10,12,12,13,13,9,8,7,7,7]})     series1  series2  series3 0               1       10 1               1       12 2               1       20 3               1       10 4               2       12 5               2        4 6        b        1        8 7        b        1        8 8        b        1        1 9        b        1       10 10       b        1       12 11       b        1       12 12       b        1       13 13       b        1       13 14       c        1        9 15       c        1        8 16       c        1        7 17       c        1        7 18       c        1        7

what need group series1 , series2 , convert values in series3 minimum of group. i.e.:

df2 = pd.dataframe({'series1':['a','a','a','a','a','a','b','b','b','b','b','b','b','b','c','c','c','c','c'],                    'series2':[1,1,1,1,2,2,1,1,1,1,1,1,1,1,1,1,1,1,1],                    'series3':[10,10,10,10,4,4,1,1,1,1,1,1,1,1,7,7,7,7,7]})     series1  series2  series3 0               1       10 1               1       10 2               1       10 3               1       10 4               2        4 5               2        4 6        b        1        1 7        b        1        1 8        b        1        1 9        b        1        1 10       b        1        1 11       b        1        1 12       b        1        1 13       b        1        1 14       c        1        7 15       c        1        7 16       c        1        7 17       c        1        7 18       c        1        7

i have feeling can done .groupby(), i'm not sure how replace in existing dataframe, or add new series.

i'm able get:

df.groupby(['series1', 'series2']).min()                    series3 series1 series2                1             10         2              4 b       1              1 c       1              7

which correct minimums per group, cant figure out simple way pop original dataframe.

you can use groupby.transform, gives same length series can assign data frame:

df['series3'] = df.groupby(['series1', 'series2']).series3.transform('min') df

enter image description here


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