fix(projection): detect numpy and polars list columns as vectors

packages/backend/embedding_atlas/projection.py

@@ -321,6 +321,11 @@ def _detect_binary_modality(data: bytes) -> str:
 
 def _infer_modality(series: nw.Series) -> str:
     """Infer the modality by inspecting the first non-null value in the series."""
+    # Typed list/array columns (e.g. polars) don't return a Python list per value
+    dtype = series.dtype
+    if isinstance(dtype, (nw.List, nw.Array)) and dtype.inner.is_numeric():
+        return "vector"
+
     non_null = series.drop_nulls()
     if len(non_null) == 0:
         return "text"
@@ -332,7 +337,7 @@ def _infer_modality(series: nw.Series) -> str:
     if (
         isinstance(sample, list)
         and len(sample) > 0
-        and isinstance(sample[0], (int, float))
+        and isinstance(sample[0], (int, float, np.number))
     ):
         return "vector"
 

packages/backend/tests/test_modality_detection.py

@@ -5,6 +5,7 @@
 import narwhals as nw
 import numpy as np
 import pandas as pd
+import polars as pl
 import pytest
 from embedding_atlas.projection import (
     _detect_binary_modality,
@@ -157,6 +158,28 @@ def test_vector_empty_list_falls_through_to_text(self):
         series = _nw_series([[], []])
         assert _infer_modality(series) == "text"
 
+    def test_vector_list_of_numpy_scalars(self):
+        vectors = np.array([[1.0, 2.0, 3.0], [4.0, 5.0, 6.0]], dtype=np.float32)
+        series = _nw_series([list(v) for v in vectors])
+        assert _infer_modality(series) == "vector"
+
+    def test_vector_polars_list(self):
+        series = nw.from_native(
+            pl.Series([[1.0, 2.0, 3.0], [4.0, 5.0, 6.0]]), series_only=True
+        )
+        assert _infer_modality(series) == "vector"
+
+    def test_vector_polars_array(self):
+        series = nw.from_native(
+            pl.Series([[1.0, 2.0], [3.0, 4.0]], dtype=pl.Array(pl.Float32, 2)),
+            series_only=True,
+        )
+        assert _infer_modality(series) == "vector"
+
+    def test_polars_list_of_strings_is_text(self):
+        series = nw.from_native(pl.Series([["a", "b"], ["c"]]), series_only=True)
+        assert _infer_modality(series) == "text"
+
     def test_image_bytes(self):
         png_bytes = b"\x89PNG\r\n\x1a\n" + b"\x00" * 20
         series = _nw_series([png_bytes, png_bytes])