Fix error in dataset_to_point_list when chain, draw are not the leading dims (#7180)

Author: OriolAbril

pymc/util.py

@@ -249,9 +249,10 @@ def dataset_to_point_list(
             raise ValueError(f"Variable names must be str, but dataset key {vn} is a {type(vn)}.")
     num_sample_dims = len(sample_dims)
     stacked_dims = {dim_name: ds[var_names[0]][dim_name] for dim_name in sample_dims}
+    transposed_dict = {vn: da.transpose(*sample_dims, ...) for vn, da in ds.items()}
     stacked_dict = {
-        vn: da.transpose(*sample_dims, ...).values.reshape((-1, *da.shape[num_sample_dims:]))
-        for vn, da in ds.items()
+        vn: da.values.reshape((-1, *da.shape[num_sample_dims:]))
+        for vn, da in transposed_dict.items()
     }
     points = [
         {vn: stacked_dict[vn][i, ...] for vn in var_names}

tests/test_util.py

@@ -170,6 +170,16 @@ def test_dataset_to_point_list(input_type):
     assert isinstance(pl[0]["A"], np.ndarray)
 
 
+def test_transposed_dataset_to_point_list():
+    ds = xarray.Dataset()
+    ds["A"] = xarray.DataArray([[[1, 2, 3], [2, 3, 4]]] * 5, dims=("team", "draw", "chain"))
+    pl, _ = dataset_to_point_list(ds, sample_dims=["chain", "draw"])
+    assert isinstance(pl, list)
+    assert len(pl) == 6
+    assert isinstance(pl[0], dict)
+    assert isinstance(pl[0]["A"], np.ndarray)
+
+
 def test_dataset_to_point_list_str_key():
     # Check that non-str keys are caught
     ds = xarray.Dataset()