Groupby column and find min and max of each group

Question

I have the following dataset,

        Day    Element  Data_Value
6786    01-01   TMAX    112
9333    01-01   TMAX    101
9330    01-01   TMIN    60
11049   01-01   TMIN    0
6834    01-01   TMIN    25
11862   01-01   TMAX    113
1781    01-01   TMAX    115
11042   01-01   TMAX    105
1110    01-01   TMAX    111
651     01-01   TMIN    44
11350   01-01   TMIN    83
1798    01-02   TMAX    70
4975    01-02   TMAX    79
12774   01-02   TMIN    0
3977    01-02   TMIN    60
2485    01-02   TMAX    73
4888    01-02   TMIN    31
11836   01-02   TMIN    26
11368   01-02   TMAX    71
2483    01-02   TMIN    26

I want to group by the Day and then find the overall min of TMIN an the max of TMAX and put these in to a data frame, so I get an output like...

Day    DayMin    DayMax
01-01  0         115
01-02  0         79

I know I need to do,

df.groupby(by='Day')

but I am a stuck with the next step - should create columns to store the TMAX and TMIN values?

Answer 1

You can use a assign + abs, followed by groupby + agg:

df = (df.assign(Data_Value=df['Data_Value'].abs())
       .groupby(['Day'])['Data_Value'].agg([('Min' , 'min'), ('Max', 'max')])
       .add_prefix('Day'))

df 
       DayMin  DayMax
Day                  
01-01       0     115
01-02       0      79