Merging two columns into one

Question

If I have one dataframe (df) with:

Columnx      Columny
1             NA
2             NA
3             NA
NA            4
NA            5
NA            6

and want

Column z
1
2
3
4
5
6

How can I do this in the simplest way possible? Essentially x and y are date columns, but due to a previous merge I have two date columns each filled with NA where the other is occupied, but only want one date column.

I think the dupe is more about fillna keeping 2 columns. This is to collapse into 1 @BEN_YO — yatu, Oct 08 '20 at 15:03
Actually you're right @ben `df.Columnx.fillna(df.Columny)` is enough, my bad — yatu, Oct 08 '20 at 16:17

score 4 · Answer 1 · answered Oct 08 '20 at 15:01

Use df.combine_first():

In [58]: df
Out[58]: 
   Column x  Column y
0       1.0       NaN
1       2.0       NaN
2       3.0       NaN
3       NaN       4.0
4       NaN       5.0
5       NaN       6.0

In [59]: df['Column x'].combine_first(df['Column y'])
Out[59]: 
0    1.0
1    2.0
2    3.0
3    4.0
4    5.0
5    6.0
Name: Column_x, dtype: float64

score 3 · Answer 2 · answered Oct 08 '20 at 15:00

3

You could use stack here:

pd.DataFrame(df.stack().to_numpy(), columns=['Columnsz'])

   Columnsz
0       1.0
1       2.0
2       3.0
3       4.0
4       5.0
5       6.0

answered Oct 08 '20 at 15:00

yatu

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Merging two columns into one

2 Answers2