Handle array names in concat

e.g. where some names may be None, or where there may be collisions with existing coordinates.

Author: Zac-HD

xarray/core/combine.py

@@ -325,16 +325,16 @@ def _dataarray_concat(arrays, dim, data_vars, coords, compat,
                          'concatenating DataArray objects')
 
     name = result_name(arrays)
-    if name is None and compat == 'identical':
+    names = [arr.name for arr in arrays]
+    if compat == 'identical' and len(set(names)) != 1:
         raise ValueError('array names not identical')
     datasets = [arr.rename(name)._to_temp_dataset() for arr in arrays]
 
-    if name is None and isinstance(dim, str) and dim not in arrays[0].dims:
-        # If we're concatenating uniquely named arrays along a new dimension,
-        # use the existing names as coordinates.
-        names = [arr.name for arr in arrays]
-        if len(set(names) - {None}) == len(names):
-            dim = pd.Index(names, name=dim)
+    if isinstance(dim, str) and len(set(names) - {None}) == len(names) \
+            and not any(dim in a.dims or dim in a.coords for a in arrays):
+        # We're concatenating arrays with unique non-None names along
+        # a new dimension, so we use the existing names as coordinates.
+        dim = pd.Index(names, name=dim)
 
     ds = _dataset_concat(datasets, dim, data_vars, coords, compat,
                          positions)