# xarray.DataArray.combine_first

#### DataArray.combine_first(other)[[source]](https://github.com/pydata/xarray/blob/main/xarray/core/dataarray.py#L3977-L3993)

Combine two DataArray objects, with union of coordinates.

This operation follows the normal broadcasting and alignment rules of
`join='outer'`.  Default to non-null values of array calling the
method.  Use np.nan to fill in vacant cells after alignment.

* **Parameters:**
  **other** ([`DataArray`](xarray.DataArray.html.md#xarray.DataArray)) – Used to fill all matching missing values in this array.
* **Returns:**
  [`DataArray`](xarray.DataArray.html.md#xarray.DataArray)