facetgrid: Ensure that colormap params are only determined once.

Fixes pydata#3569

doc/whats-new.rst

@@ -48,7 +48,8 @@ Bug fixes
 - Fix a regression where deleting a coordinate from a copied :py:class:`DataArray`
   can affect the original :py:class:`Dataarray`.  (:issue:`3899`, :pull:`3871`)
   By `Todd Jennings <https://github.com/toddrjen>`_
-
+- Ensure that colormap parameters are only determined once for FacetGrid plots.
+  (:issue:`3569`). By `Deepak Cherian <https://github.com/dcherian>`_
 
 Documentation
 ~~~~~~~~~~~~~

xarray/plot/facetgrid.py

@@ -273,7 +273,7 @@ def map_dataarray(self, func, x, y, **kwargs):
             # None is the sentinel value
             if d is not None:
                 subset = self.data.loc[d]
-                mappable = func(subset, x=x, y=y, ax=ax, **func_kwargs)
+                mappable = func(subset, x=x, y=y, ax=ax, **func_kwargs, _is_facetgrid=True)
                 self._mappables.append(mappable)
 
         self._finalize_grid(x, y)

xarray/plot/plot.py

@@ -692,7 +692,10 @@ def newplotfunc(
         _ensure_plottable(xplt, yplt)
 
         cmap_params, cbar_kwargs = _process_cmap_cbar_kwargs(
-            plotfunc, zval.data, **locals()
+            plotfunc,
+            zval.data,
+            **locals(),
+            _is_facetgrid=kwargs.pop("_is_facetgrid", False),
         )
 
         if "contour" in plotfunc.__name__:

xarray/plot/utils.py

@@ -153,6 +153,7 @@ def _determine_cmap_params(
     levels=None,
     filled=True,
     norm=None,
+    _is_facetgrid=False,
 ):
     """
     Use some heuristics to set good defaults for colorbar and range.
@@ -727,6 +728,7 @@ def _process_cmap_cbar_kwargs(
     colors=None,
     cbar_kwargs: Union[Iterable[Tuple[str, Any]], Mapping[str, Any]] = None,
     levels=None,
+    _is_facetgrid=False,
     **kwargs,
 ):
     """
@@ -773,6 +775,12 @@ def _process_cmap_cbar_kwargs(
 
     cmap_args = getfullargspec(_determine_cmap_params).args
     cmap_kwargs.update((a, kwargs[a]) for a in cmap_args if a in kwargs)
-    cmap_params = _determine_cmap_params(**cmap_kwargs)
+    if not _is_facetgrid:
+        cmap_params = _determine_cmap_params(**cmap_kwargs)
+    else:
+        cmap_params = {
+            k: cmap_kwargs[k]
+            for k in ["vmin", "vmax", "cmap", "extend", "levels", "norm"]
+        }
 
     return cmap_params, cbar_kwargs