I have a dataframe df with the following structure

   Floor         Room  Area
0      1  Living room    25
1      1      Kitchen    20
2      1      Bedroom    15
3      2     Bathroom    21
4      2      Bedroom    14

and I want to add a series floor_share with the relative share/ratio of the given floor, so that the dataframe becomes

   Floor         Room  Area  floor_share
0      1  Living room    18         0,30
1      1      Kitchen    18         0,30
2      1      Bedroom    24         0,40
3      2     Bathroom    10         0,67         
4      2      Bedroom    20         0,33

If it is possible to do this with a one-liner (or any other idiomatic manner), I’ll be very happy to learn how.

Current workaround

What I have done that produces the correct results is to first find the total floor areas by

floor_area_sums = df.groupby('Floor')['Area'].sum()

which gives

Floor
1    60
2    35
Name: Area, dtype: int64

I then initialize a new series to 0, and find the correct values while iterating through the dataframe rows.

df["floor_share"] = 0
for idx, row in df.iterrows():
    df.loc[idx, 'floor_share'] = df.loc[idx, 'Area']/floor_area_sums[row.Floor]

>Solution :

IIUC use:

df["floor_share"] = df['Area'].div(df.groupby('Floor')['Area'].transform('sum'))
print (df)
   Floor         Room  Area  floor_share
0      1  Living room    18     0.300000
1      1      Kitchen    18     0.300000
2      1      Bedroom    24     0.400000
3      2     Bathroom    10     0.333333
4      2      Bedroom    20     0.666667