python pandas lambda with 2 and more variables

Question

I have a dataframe where I'd like to add a column with conditional sum of values based on criteria in 2 (possibly 3) different columns. I'm trying to use lambda function such as:

df['newColumn'] = df[['colA','colB']].apply(lambda x,y: 
df.loc[df['colA']==x].loc[df['colB']==y]['Total Amount'].sum())

This approach doesn't work although when I test the .loc statement separately and use values in lieu of x and y I do get the correct sum. I would like to bring in another column to this if possible. The error Im getting is: "() missing 1 required positional argument: 'y'", 'occurred at index colA. Any help greatly appreciated,

Can you add some sample data and expected output? – jezrael Nov 08 '18 at 12:23 — jezrael, Nov 08 '18 at 12:23

zipa · Accepted Answer · 2018-11-08T12:27:36.160

0

My guess is you want this:

df = pd.DataFrame({'A': [1,1,2,2,3,3],
                   'B': [2,2,2,3,3,3],
                   'TotalAmount': [10,20,30,40,50,60]})

df['NewColumn'] = df.groupby(['A', 'B'])['TotalAmount'].transform('sum')
df
#   A  B  TotalAmount  NewColumn
#0  1  2           10         30
#1  1  2           20         30
#2  2  2           30         30
#3  2  3           40         40
#4  3  3           50        110
#5  3  3           60        110

edited Nov 08 '18 at 12:27

answered Nov 08 '18 at 12:26

zipa

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@jezrael I believe I deserve points for deciphering :) – zipa Nov 08 '18 at 12:28
thanks! is there a way in python 3 to do this using lambda expression? – whada Nov 08 '18 at 17:26

python pandas lambda with 2 and more variables

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