# pandas.DataFrame.combine_first

`DataFrame.``combine_first`(other)

  Update null elements with value in the same location in other.

  Combine two DataFrame objects by filling null values in one DataFrame with non-null values from other DataFrame. The row and column indexes of the resulting DataFrame will be the union of the two.

  Parameters:

  other : DataFrame

  > Provided DataFrame to use to fill null values.

  Returns: | DataFrame

  See also

  `DataFrame.combine`
    Perform series-wise operation on two DataFrames using a given function.

  Examples

      >>> df1 = pd.DataFrame({'A': [None, 0], 'B': [None, 4]})
      >>> df2 = pd.DataFrame({'A': [1, 1], 'B': [3, 3]})
      >>> df1.combine_first(df2)
           A    B
      0  1.0  3.0
      1  0.0  4.0

  Null values still persist if the location of that null value does not exist in other

      >>> df1 = pd.DataFrame({'A': [None, 0], 'B': [4, None]})
      >>> df2 = pd.DataFrame({'B': [3, 3], 'C': [1, 1]}, index=[1, 2])
      >>> df1.combine_first(df2)
           A    B    C
      0  NaN  4.0  NaN
      1  0.0  3.0  1.0
      2  NaN  3.0  1.0

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