1

I have a dataframe such as ::

Group COL1 COL2 
G1    30   500
G1    21   500 
G1    43   500 
G2    89   677
G2    78   900 
G3    32   322
G3    90   200

and I would like to add a new column called mean_group where I calculate for each Group, the sum of COL1/unique value of COL2.For instance, (30+21+43)/500 = 0.188

I should then get:  
Group COL1 COL2 mean_group
G1    30   500  0.188
G1    21   500  0.188
G1    43   500  0.188
G2    89   677  0.2466765
G2    78   677  0.2466765
G3    32   322  0.09937888
chippycentra
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  • https://stackoverflow.com/questions/30244952/how-do-i-create-a-new-column-from-the-output-of-pandas-groupby-sum This is similar concept – Arunbh Yashaswi Jan 05 '22 at 18:36

2 Answers2

2

do this

df['mean_group']=df.groupby('Group')['COL1'].transform('sum')/df['COL2']

output:

  Group  COL1  COL2  mean_group
0    G1    30   500    0.188000
1    G1    21   500    0.188000
2    G1    43   500    0.188000
3    G2    89   677    0.246677
4    G2    78   900    0.185556
5    G3    32   322    0.378882
6    G3    90   200    0.610000
gilf0yle
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1

Use:

df['mean_group'] = df.groupby('Group')['COL1'].transform('mean')/df['COL2']
mozway
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