fixes, and another test

src/levanter/data/sharded_datasource.py

@@ -249,8 +249,10 @@ def open_shard_at_row(self, shard_name: str, row: int) -> Iterator[str]:
                     if row >= total_rows:
                         return iter([])
 
+                    num_row_groups = parquet_file.metadata.num_row_groups
+
                     # Compute cumulative row counts
-                    row_counts = [rg.num_rows for rg in parquet_file.metadata.row_groups]
+                    row_counts = [parquet_file.metadata.row_group(i).num_rows for i in range(num_row_groups)]
                     cumulative_rows = [0]
                     for count in row_counts:
                         cumulative_rows.append(cumulative_rows[-1] + count)
@@ -465,8 +467,10 @@ def open_shard_at_row(self, shard_name: str, row: int) -> Iterator[dict]:
             if row >= total_rows:
                 return iter([])
 
-            # compute cumulative row counts
-            row_counts = [rg_meta.num_rows for rg_meta in parquet_file.metadata.row_groups]
+            num_row_groups = parquet_file.metadata.num_row_groups
+
+            # Compute cumulative row counts
+            row_counts = [parquet_file.metadata.row_group(i).num_rows for i in range(num_row_groups)]
             cumulative_rows = [0]
             for count in row_counts:
                 cumulative_rows.append(cumulative_rows[-1] + count)

tests/test_sharded_dataset.py

@@ -1,7 +1,12 @@
 import os
 import tempfile
 
-from levanter.data.sharded_datasource import AudioTextUrlDataSource, ParquetDataSource, _sniff_format_for_dataset
+from levanter.data.sharded_datasource import (
+    AudioTextUrlDataSource,
+    ParquetDataSource,
+    _sniff_format_for_dataset,
+    TextUrlDataSource,
+)
 from test_utils import skip_if_no_soundlibs
 
 
@@ -68,3 +73,29 @@ def test_basic_parquet_datasource_read_row():
         assert row_data[0]["column2"] == 20
         assert row_data[1]["column1"] == "value3"
         assert row_data[1]["column2"] == 30
+
+
+def test_text_url_data_source_parquet():
+    import pyarrow as pa
+    import pyarrow.parquet as pq
+
+    with tempfile.NamedTemporaryFile(suffix=".parquet", delete=True) as f:
+        data = {
+            "text": ["line1", "line2", "line3", "line4", "line5", "line6"],
+            "column2": [10, 20, 30, 40, 50, 60],
+        }
+        table = pa.Table.from_pydict(data)
+        pq.write_table(table, f.name)
+
+        datasource = TextUrlDataSource([os.path.abspath(f.name)], text_key="text")
+
+        assert len(datasource.shard_names) == 1, "Expected only one shard"
+        shard_name = datasource.shard_names[0]
+
+        # Read data starting from row 2
+        row_data = list(datasource.open_shard_at_row(shard_name=shard_name, row=2))
+
+        # Verify the output
+        expected_texts = ["line3", "line4", "line5", "line6"]
+        assert len(row_data) == len(expected_texts), f"Expected {len(expected_texts)} rows starting from index 2"
+        assert row_data == expected_texts, f"Expected texts {expected_texts}, got {row_data}"