fix: Infer correct number of components in gaze init

src/pymovements/gaze/gaze_dataframe.py

@@ -187,55 +187,31 @@ def __init__(
         if time_column is not None:
             self.frame = self.frame.rename({time_column: 'time'})
 
-        n_components = None
+        # List of passed not-None column specifier lists.
+        # The list will be used for inferring n_components.
+        column_specifiers: list[list[str]] = []
+
         if pixel_columns:
-            _check_component_columns(
-                frame=self.frame,
-                pixel_columns=pixel_columns,
-            )
-            self.nest(
-                input_columns=pixel_columns,
-                output_column='pixel',
-            )
-            n_components = len(pixel_columns)
+            _check_component_columns(self.frame, pixel_columns=pixel_columns)
+            self.nest(pixel_columns, output_column='pixel')
+            column_specifiers.append(pixel_columns)
 
         if position_columns:
-            _check_component_columns(
-                frame=self.frame,
-                position_columns=position_columns,
-            )
-
-            self.nest(
-                input_columns=position_columns,
-                output_column='position',
-            )
-            n_components = len(position_columns)
+            _check_component_columns(self.frame, position_columns=position_columns)
+            self.nest(position_columns, output_column='position')
+            column_specifiers.append(position_columns)
 
         if velocity_columns:
-            _check_component_columns(
-                frame=self.frame,
-                velocity_columns=velocity_columns,
-            )
-
-            self.nest(
-                input_columns=velocity_columns,
-                output_column='velocity',
-            )
-            n_components = len(velocity_columns)
+            _check_component_columns(self.frame, velocity_columns=velocity_columns)
+            self.nest(velocity_columns, output_column='velocity')
+            column_specifiers.append(velocity_columns)
 
         if acceleration_columns:
-            _check_component_columns(
-                frame=self.frame,
-                acceleration_columns=acceleration_columns,
-            )
+            _check_component_columns(self.frame, acceleration_columns=acceleration_columns)
+            self.nest(acceleration_columns, output_column='acceleration')
+            column_specifiers.append(acceleration_columns)
 
-            self.nest(
-                input_columns=acceleration_columns,
-                output_column='acceleration',
-            )
-            n_components = len(acceleration_columns)
-
-        self.n_components = n_components
+        self.n_components = _infer_n_components(self.frame, column_specifiers)
         self.experiment = experiment
 
     def transform(
@@ -397,6 +373,8 @@ def nest(
         output_column:
             Name of the resulting tuple column.
         """
+        _check_component_columns(frame=self.frame, **{output_column: input_columns})
+
         self.frame = self.frame.with_columns(
             pl.concat_list([pl.col(component) for component in input_columns])
             .alias(output_column),
@@ -526,3 +504,48 @@ def _check_n_components(n_components: Any) -> None:
     """Check that n_components is either 2, 4 or 6."""
     if n_components not in {2, 4, 6}:
         raise AttributeError(f'n_components must be either 2, 4 or 6 but is {n_components}')
+
+
+def _infer_n_components(frame: pl.DataFrame, column_specifiers: list[list[str]]) -> int | None:
+    """Infer number of components from DataFrame.
+
+    Method checks nested columns `pixel`, `position`, `velocity` and `acceleration` for number of
+    components by getting their list lenghts, which must be equal for all else a ValueError is
+    raised. Additionally, a list of list of column specifiers is checked for consistency.
+
+    Parameters
+    ----------
+    frame: pl.DataFrame
+        DataFrame to check.
+    column_specifiers:
+        List of list of column specifiers.
+
+    Returns
+    -------
+    int or None
+        Number of components
+
+    Raises
+    ------
+    ValueError
+        If number of components is not equal for all considered columns and rows.
+    """
+    all_considered_columns = ['pixel', 'position', 'velocity', 'acceleration']
+    considered_columns = [column for column in all_considered_columns if column in frame.columns]
+
+    list_lengths = {
+        list_length
+        for column in considered_columns
+        for list_length in frame.get_column(column).list.lengths().unique().to_list()
+    }
+
+    for column_specifier_list in column_specifiers:
+        list_lengths.add(len(column_specifier_list))
+
+    if len(list_lengths) > 1:
+        raise ValueError(f'inconsistent number of components inferred: {list_lengths}')
+
+    if len(list_lengths) == 0:
+        return None
+
+    return next(iter(list_lengths))