How to add two dataframes by specifying only some columns for addition

Question

Here is the code:

input:

df1 = pd.DataFrame({'a': [1,2,3], 'b': [2,3,4], 'c':['aa','bb','cc'], 'd':[5,9,1]})

df2 = pd.DataFrame({'a': [4,5,6], 'b': [7,8,9], 'c':['dd','ee','ff'], 'd':[50,90,10]})


combinedframes_add = df1.add(df2, fill_value=0)

output:

   a   b     c   d
0  5   9  aadd  55
1  7  11  bbee  99
2  9  13  ccff  11

But I want my output to like this:

   a   b     c   d
0  1   9  aadd  55
1  2  11  bbee  99
2  3  13  ccff  11

'a' column should not be added, it should remain the same as in df1.

How can I achieve that?

Thanks in advance.

jezrael · Accepted Answer · 2019-12-06 07:22:34Z

2

One idea is remove column a from second DataFrame:

combinedframes_add = df1.add(df2.drop('a', axis=1), fill_value=0)
print (combinedframes_add)
     a   b     c   d
0  1.0   9  aadd  55
1  2.0  11  bbee  99
2  3.0  13  ccff  11

Or set 0 to column a:

combinedframes_add = df1.add(df2.assign(a=0), fill_value=0)
print (combinedframes_add)
   a   b     c   d
0  1   9  aadd  55
1  2  11  bbee  99
2  3  13  ccff  11

answered Dec 6, 2019 at 7:22

jezrael

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