only change column order when needed

python-package/lightgbm/basic.py

@@ -519,12 +519,13 @@ def _data_from_pandas(data, feature_name, categorical_feature, pandas_categorica
         if feature_name == 'auto' or feature_name is None:
             data = data.rename(columns=str)
         elif isinstance(feature_name, list) and is_predict:
-            features_df = data.columns.astype(str).tolist()
-            missing_features = set(feature_name) - set(features_df)
+            df_features = [str(x) for x in data.columns]
+            missing_features = set(feature_name) - set(df_features)
             if missing_features:
                 raise ValueError(f'The following features are missing: {missing_features}')
-            sort_idxs = [features_df.index(feature) for feature in feature_name]
-            data = data.iloc[:, sort_idxs]  # ensure column order
+            sort_idxs = [df_features.index(feature) for feature in feature_name]
+            if not all(x == i for i, x in enumerate(sort_idxs)):
+                data = data.iloc[:, sort_idxs]  # ensure column order
         cat_cols = [col for col, dtype in zip(data.columns, data.dtypes) if isinstance(dtype, pd_CategoricalDtype)]
         cat_cols_not_ordered = [col for col in cat_cols if not data[col].cat.ordered]
         if pandas_categorical is None:  # train dataset