Begin support for combine, merge.

Author: dcherian

xarray/core/combine.py

@@ -243,6 +243,7 @@ def _combine_1d(
                 dim=concat_dim,
                 data_vars=data_vars,
                 coords=coords,
+                compat=compat,
                 fill_value=fill_value,
                 join=join,
             )
@@ -592,6 +593,7 @@ def combine_by_coords(
             concat_dims=concat_dims,
             data_vars=data_vars,
             coords=coords,
+            compat=compat,
             fill_value=fill_value,
             join=join,
         )
@@ -823,6 +825,7 @@ def _old_auto_combine(
                 dim=dim,
                 data_vars=data_vars,
                 coords=coords,
+                compat=compat,
                 fill_value=fill_value,
                 join=join,
             )
@@ -841,6 +844,7 @@ def _auto_concat(
     coords="different",
     fill_value=dtypes.NA,
     join="outer",
+    compat="no_conflicts"
 ):
     if len(datasets) == 1 and dim is None:
         # There is nothing more to combine, so kick out early.
@@ -867,5 +871,6 @@ def _auto_concat(
                 )
             dim, = concat_dims
         return concat(
-            datasets, dim=dim, data_vars=data_vars, coords=coords, fill_value=fill_value
+            datasets, dim=dim, data_vars=data_vars, coords=coords, fill_value=fill_value,
+            compat=compat
         )

xarray/core/merge.py

@@ -44,6 +44,7 @@
         "broadcast_equals": 2,
         "minimal": 3,
         "no_conflicts": 4,
+        "override": 5,
     }
 )
 
@@ -81,7 +82,7 @@ def unique_variable(name, variables, compat="broadcast_equals"):
     variables : list of xarray.Variable
         List of Variable objects, all of which go by the same name in different
         inputs.
-    compat : {'identical', 'equals', 'broadcast_equals', 'no_conflicts'}, optional
+    compat : {'identical', 'equals', 'broadcast_equals', 'no_conflicts', 'override'}, optional
         Type of equality check to use.
 
     Returns
@@ -106,17 +107,20 @@ def unique_variable(name, variables, compat="broadcast_equals"):
         if compat == "no_conflicts":
             combine_method = "fillna"
 
-        for var in variables[1:]:
-            if not getattr(out, compat)(var):
-                raise MergeError(
-                    "conflicting values for variable %r on "
-                    "objects to be combined:\n"
-                    "first value: %r\nsecond value: %r" % (name, out, var)
-                )
-            if combine_method:
-                # TODO: add preservation of attrs into fillna
-                out = getattr(out, combine_method)(var)
-                out.attrs = var.attrs
+        if compat == "override":
+            out = variables[0]
+        else:
+            for var in variables[1:]:
+                if not getattr(out, compat)(var):
+                    raise MergeError(
+                        "conflicting values for variable %r on "
+                        "objects to be combined:\n"
+                        "first value: %r\nsecond value: %r" % (name, out, var)
+                    )
+                if combine_method:
+                    # TODO: add preservation of attrs into fillna
+                    out = getattr(out, combine_method)(var)
+                    out.attrs = var.attrs
 
     return out
 
@@ -152,7 +156,7 @@ def merge_variables(
     priority_vars : mapping with Variable or None values, optional
         If provided, variables are always taken from this dict in preference to
         the input variable dictionaries, without checking for conflicts.
-    compat : {'identical', 'equals', 'broadcast_equals', 'minimal', 'no_conflicts'}, optional
+    compat : {'identical', 'equals', 'broadcast_equals', 'minimal', 'no_conflicts', 'override'}, optional
         Type of equality check to use when checking for conflicts.
 
     Returns
@@ -449,7 +453,7 @@ def merge_core(
     ----------
     objs : list of mappings
         All values must be convertable to labeled arrays.
-    compat : {'identical', 'equals', 'broadcast_equals', 'no_conflicts'}, optional
+    compat : {'identical', 'equals', 'broadcast_equals', 'no_conflicts', 'override'}, optional
         Compatibility checks to use when merging variables.
     join : {'outer', 'inner', 'left', 'right'}, optional
         How to combine objects with different indexes.