fix: use_columns no longer silently fails when leftmost columns are empty (#438)

Author: stephenlf

python/tests/test_column_selection.py

@@ -857,3 +857,55 @@ def test_use_columns_with_table_and_provided_columns() -> None:
 
     pd_df = table.to_pandas()
     pd_assert_frame_equal(pd_df, expected_pd_df)
+
+
+def test_use_column_range_with_offset_without_table():
+    excel_reader = fastexcel.read_excel(path_for_fixture("sheet-and-table-with-offset.xlsx"))
+
+    sheet = excel_reader.load_sheet("without-table", use_columns="H:I", header_row=9)
+
+    expected_pl_df = pl.DataFrame(
+        {
+            "Column at H10": [1, 2, 3],
+            "Column at I10": [4, 5, 6],
+        }
+    )
+
+    expected_pd_df = pd.DataFrame(
+        {
+            "Column at H10": [1, 2, 3],
+            "Column at I10": [4, 5, 6],
+        }
+    )
+
+    pl_df = sheet.to_polars()
+    pl_assert_frame_equal(pl_df, expected_pl_df, check_dtypes=False)
+
+    pd_df = sheet.to_pandas()
+    pd_assert_frame_equal(pd_df, expected_pd_df, check_dtype=False)
+
+
+def test_use_column_range_with_offset_with_table():
+    excel_reader = fastexcel.read_excel(path_for_fixture("sheet-and-table-with-offset.xlsx"))
+
+    sheet = excel_reader.load_sheet("with-table", use_columns="D:E", header_row=4)
+
+    expected_pl_df = pl.DataFrame(
+        {
+            "Column at D5": [1, 2, 3, 4],
+            "Column at E5": [4, 5, 6, 8],
+        }
+    )
+
+    expected_pd_df = pd.DataFrame(
+        {
+            "Column at D5": [1, 2, 3, 4],
+            "Column at E5": [4, 5, 6, 8],
+        }
+    )
+
+    pl_df = sheet.to_polars()
+    pl_assert_frame_equal(pl_df, expected_pl_df, check_dtypes=False)
+
+    pd_df = sheet.to_pandas()
+    pd_assert_frame_equal(pd_df, expected_pd_df, check_dtype=False)

src/types/excelsheet/column_info/mod.rs

@@ -180,8 +180,8 @@ impl ColumnInfoNoDtype {
         &self.name
     }
 
-    pub(super) fn index(&self) -> usize {
-        self.index
+    pub(super) fn absolute_index(&self) -> usize {
+        self.absolute_index
     }
 
     fn dtype_info<D: CalamineDataProvider>(

src/types/excelsheet/mod.rs

@@ -183,7 +183,8 @@ impl SelectedColumns {
                         match selected_column {
                             IdxOrName::Idx(index) => available_columns
                                 .iter()
-                                .position(|col_info| &col_info.index() == index),
+                                // Sheets have absolute column names (A, B, C, ...)
+                                .position(|col_info| &col_info.absolute_index() == index),
                             IdxOrName::Name(name) => available_columns
                                 .iter()
                                 .position(|col_info| col_info.name() == name.as_str()),