How can I use a value from one column to populate a nan in another column and viceversa in Pandas?

Question

There are 2 columns in my Pandas dataframe.

cola    colb  
X         X     
C        NaN    
NaN       R     
X         X

I want to get rid of cola and colb and replace it with colc.

cola    colb   colc
X         X     X
C        NaN    C
NaN       R     R
X         X     X

Basically I need to populate colc with the value in cola and colb. If there is a nan in cola then it will pull from colb and if there is a nan in colb it will pull from cola. cola and colb should always be equal if it doesn't have a nan in one of them.

How would I achieve this in pandas?

score 3 · Accepted Answer · answered Jul 07 '20 at 20:34

3

df["colc"] = df["cola"].fillna(df["colb"])

answered Jul 07 '20 at 20:34

Toby Petty

4,431
1
17
29

score 1 · Answer 2 · answered Jul 07 '20 at 20:38

1

Alternatively, use np.where to create logical conditions to fill your array:

df["colc"] = np.where(df["cola"].notna(),df["cola"],df["colb"])

answered Jul 07 '20 at 20:38

Yaakov Bressler

9,056
2
45
69

How can I use a value from one column to populate a nan in another column and viceversa in Pandas?

2 Answers2