From c7a81b98bc556569a15ce01aedbd8524ccc06c08 Mon Sep 17 00:00:00 2001
From: David Hoese <david.hoese@ssec.wisc.edu>
Date: Sun, 9 Jun 2019 20:30:42 -0500
Subject: [PATCH] Fix 'to_masked_array' computing dask arrays twice

---
 xarray/core/dataarray.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/xarray/core/dataarray.py b/xarray/core/dataarray.py
index cab5612dfe1..ce92641203d 100644
--- a/xarray/core/dataarray.py
+++ b/xarray/core/dataarray.py
@@ -1746,8 +1746,9 @@ def to_masked_array(self, copy=True):
         result : MaskedArray
             Masked where invalid values (nan or inf) occur.
         """
-        isnull = pd.isnull(self.values)
-        return np.ma.MaskedArray(data=self.values, mask=isnull, copy=copy)
+        values = self.values  # only compute lazy arrays once
+        isnull = pd.isnull(values)
+        return np.ma.MaskedArray(data=values, mask=isnull, copy=copy)
 
     def to_netcdf(self, *args, **kwargs):
         """Write DataArray contents to a netCDF file.