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# Pandas DataFrame | combine_first method

schedule Aug 10, 2023
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Pandas `DataFrame.combine_first(~)` method replaces all instances of `NaN` in one DataFrame with non-`NaN` values from the other DataFrame.

Note the following:

• only columns that share the same column label will be combined.

• if both values are `NaN`, then the result will simply be `NaN`.

# Parameters

1. `other`link | `DataFrame`

The other DataFrame to combine with.

# Return Value

A new `DataFrame`.

# Examples

## Basic usage

Consider the following DataFrames:

``` df = pd.DataFrame({"A":[None,4], "B":[5,6]})df_other = pd.DataFrame({"A":[1,8], "B":[2,pd.np.NaN], "C":[4,2]}) A B | A B C0 NaN 5 | 0 1 2 41 4 6 | 1 8 NaN 2 ```

To replace all instances of `NaN` in `df` with the corresponding values from `df_other`:

``` df.combine_first(df_other) A B C0 1.0 5 4.01 4.0 6 2.0 ```

Notice how column `C`, which did not exist in `df`, has been appended.

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