fix

flox/core.py

@@ -365,16 +365,6 @@ def find_group_cohorts(
     if not is_duck_array(labels):
         labels = np.asarray(labels)
 
-    if is_duck_dask_array(labels):
-        import dask
-
-        ((bitmask, nlabels, ilabels),) = dask.compute(
-            dask.delayed(_compute_label_chunk_bitmask)(labels, chunks)
-        )
-    else:
-        bitmask, nlabels, ilabels = _compute_label_chunk_bitmask(labels, chunks)
-
-    shape = tuple(sum(c) for c in chunks)
     nchunks = math.prod(len(c) for c in chunks)
 
     # assumes that `labels` are factorized
@@ -387,8 +377,14 @@ def find_group_cohorts(
     if nchunks == 1:
         return "blockwise", {(0,): list(range(nlabels))}
 
-    labels = np.broadcast_to(labels, shape[-labels.ndim :])
-    bitmask = _compute_label_chunk_bitmask(labels, chunks, nlabels)
+    if is_duck_dask_array(labels):
+        import dask
+
+        ((bitmask, nlabels, ilabels),) = dask.compute(
+            dask.delayed(_compute_label_chunk_bitmask)(labels, chunks, nlabels)
+        )
+    else:
+        bitmask, nlabels, ilabels = _compute_label_chunk_bitmask(labels, chunks, nlabels)
 
     CHUNK_AXIS, LABEL_AXIS = 0, 1
     chunks_per_label = bitmask.sum(axis=CHUNK_AXIS)