Merge 2 Columns In Pandas Into One Columns That Have Data In Python

I'm not sure How to word this but I'm trying to combine 2 columns say from datafram df : x1 x2 NaN 3 2 2 4 2 NaN 5 8 NaN so I would like to get result of X 3 2 4 5 8

Solution 1:

It's not clear from your question whether you want x1 to dominate over x2 (my first guess) or whether you want the maximum of both columns (@RobStarling's guess). We can do either. To see the difference, we'll change your frame slightly:

>>> df = pd.DataFrame({'x1': {0: np.nan, 1: 2.0, 2: 4.0, 3: 1, 4: 8.0}, 'x2': {0: 3.0, 1: 2.0, 2: 2.0, 3: 5.0, 4: np.nan}})
>>> df
   x1  x2
0 NaN   3
1   2   2
2   4   2
3   1   5
4   8 NaN

[5 rows x 2 columns]

If you want x1 to win, we can use where-- we want to use x1 wherever it's not null, and x2 otherwise:

>>> df["x1"].where(~pd.isnull(df["x1"]), df["x2"])
0    3
1    2
2    4
3    1
4    8
Name: x1, dtype: float64

If you want the maximum of either:

>>> df[["x1", "x2"]].max(axis=1)
0    3
1    2
2    4
3    5
4    8
dtype: float64