# pandas.Series.combine_first

`Series.``combine_first`(other)

  Combine Series values, choosing the calling Series’s values first. Result index will be the union of the two indexes

  Parameters: | other : Series
  Returns: | combined : Series

  See also

  `Series.combine`
    Perform elementwise operation on two Series using a given function

  Examples

      >>> s1 = pd.Series([1, np.nan])
      >>> s2 = pd.Series([3, 4])
      >>> s1.combine_first(s2)
      0    1.0
      1    4.0
      dtype: float64

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