Refactored code structure.

evalml/pipelines/utils.py

@@ -1381,7 +1381,6 @@ def unstack_multiseries(
     # Perform the unstacking
     X_unstacked_cols = []
     y_unstacked_cols = []
-    new_time_index = None
     for s_id in series_id_unique:
         single_series = full_dataset[full_dataset[series_id] == s_id]
 
@@ -1478,36 +1477,22 @@ def stack_X(X, series_id_name, time_index, starting_index=None, series_id_values
     """
     original_columns = set()
     series_ids = series_id_values or set()
-    for col in X.columns:
-        if col == time_index:
-            continue
-        separated_name = col.split("_")
-        original_columns.add("_".join(separated_name[:-1]))
-        if series_id_values is None:
+    if series_id_values is None:
+        for col in X.columns:
+            if col == time_index:
+                continue
+            separated_name = col.split("_")
+            original_columns.add("_".join(separated_name[:-1]))
             series_ids.add(separated_name[-1])
 
-    restacked_X = []
-
     if len(series_ids) == 0:
         raise ValueError(
-            "Unable to stack X as X had no exogenous variables and `series_id_values` is None.",
+            "X has no exogenous variables and `series_id_values` is None.",
         )
 
-    for i, original_col in enumerate(original_columns):
-        # Only include the series id once (for the first column)
-        include_series_id = i == 0
-        subset_X = [col for col in X.columns if original_col in col]
-        restacked_X.append(
-            stack_data(
-                X[subset_X],
-                include_series_id=include_series_id,
-                series_id_name=series_id_name,
-                starting_index=starting_index,
-            ),
-        )
     time_index_col = X[time_index].repeat(len(series_ids)).reset_index(drop=True)
 
-    if len(restacked_X) == 0:
+    if len(original_columns) == 0:
         start_index = starting_index or X.index[0]
         stacked_index = pd.RangeIndex(
             start=start_index,
@@ -1522,6 +1507,20 @@ def stack_X(X, series_id_name, time_index, starting_index=None, series_id_values
             index=stacked_index,
         )
     else:
+        restacked_X = []
+        for i, original_col in enumerate(original_columns):
+            # Only include the series id once (for the first column)
+            include_series_id = i == 0
+            subset_X = [col for col in X.columns if original_col in col]
+            restacked_X.append(
+                stack_data(
+                    X[subset_X],
+                    include_series_id=include_series_id,
+                    series_id_name=series_id_name,
+                    starting_index=starting_index,
+                ),
+            )
+
         restacked_X = pd.concat(restacked_X, axis=1)
         time_index_col.index = restacked_X.index
         restacked_X[time_index] = time_index_col

evalml/tests/pipeline_tests/test_pipeline_utils.py

@@ -1478,7 +1478,7 @@ def test_stack_X(
 
         with pytest.raises(
             ValueError,
-            match="Unable to stack X as X had no exogenous variables and `series_id_values` is None.",
+            match="X has no exogenous variables and `series_id_values` is None.",
         ):
             stack_X(X, "series_id", "date", starting_index=starting_index)