Sum 2 columns of pandas DataFrame with a row condition

Question

    A   B   C
0   0   -2  1
1   1   -1  2
2   2   0   3
3   3   1   0
4   4   2   5

I want to get a new column such that it picks elements from B if B is positive (>0) otherwise picks elements from C

    A   B   C    D
0   0   -2  1    1
1   1   -1  2    2 
2   2   0   3    3
3   3   1   0    1  
4   4   2   5    5

Can you clarify exactly what you want? Does it have to sum B and C (eg row 4 -> 2 + 5 is not 5), or just the maximum of both columns? — joris
– joris, Commented Mar 19, 2014 at 14:03
I want to get a new column such that it picks elements from B if B is positive (>0) otherwise picks elements from C — Rahuketu86
– Rahuketu86, Commented Mar 19, 2014 at 14:09
Also what should be done to get something like D(x) = B(x) +C(x) if B(x)>0 else C(x) — Rahuketu86
– Rahuketu86, Commented Mar 19, 2014 at 14:10
Yeah That was a follow up question. May be I will creste a new question and post it back — Rahuketu86
– Rahuketu86, Commented Mar 19, 2014 at 14:35

TomAugspurger · Accepted Answer · 2014-03-19 14:09:36Z

2

Use a Boolean mask:

In [14]: df[df[['B', 'C']] > 0].max(1)
Out[14]: 
0    1
1    2
2    3
3    1
4    5
dtype: float64

In [15]: df['D'] = df[df[['B', 'C']] > 0].max(1)

answered Mar 19, 2014 at 14:09

TomAugspurger

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1 Comment

Thanks ! any ideas how to do D(x) = B(x) +C(x) if B(x)>0 else C(x) efficiently