104 Add Grid model and segment_strokes utility function

src/graphomotor/core/models.py

@@ -191,6 +191,116 @@ def contains_points(self, points: pd.DataFrame) -> bool:
         )
 
 
+@dataclasses.dataclass
+class Grid:
+    """Represents a rectangular grid composed of multiple GridCell objects.
+
+    The grid divides a bounding box into rows and columns, where each cell can
+    hold strokes assigned by centroid location. Cells are ordered left-to-right,
+    top-to-bottom (row-major order).
+
+    Attributes:
+        cells: List of GridCell objects that compose the grid.
+    """
+
+    cells: List[GridCell] = dataclasses.field(default_factory=list)
+
+    @classmethod
+    def from_bbox(
+        cls,
+        x_min: float,
+        x_max: float,
+        y_min: float,
+        y_max: float,
+        n_rows: int,
+        n_cols: int,
+        labels: Optional[List[str]] = None,
+        padding: float = 0.1,
+    ) -> "Grid":
+        """Create a Grid by subdividing a bounding box into rows and columns.
+
+        Cells are generated in row-major order (left-to-right, top-to-bottom).
+        A small padding is added to the outer boundaries so that centroids
+        falling exactly on the outermost edge are still captured by a cell.
+
+        Args:
+            x_min: Left boundary of the bounding box.
+            x_max: Right boundary of the bounding box.
+            y_min: Bottom boundary of the bounding box.
+            y_max: Top boundary of the bounding box.
+            n_rows: Number of rows in the grid.
+            n_cols: Number of columns in the grid.
+            labels: Optional list of labels for each cell, assigned in
+                row-major order. Must have length n_rows * n_cols if provided.
+            padding: Amount to extend the outer boundaries to capture edge
+                centroids (default 0.1).
+
+        Returns:
+            A Grid instance populated with GridCell objects.
+
+        Raises:
+            ValueError: If n_rows or n_cols is less than 1, or if the length
+                of labels does not match n_rows * n_cols.
+        """
+        if n_rows < 1 or n_cols < 1:
+            raise ValueError("n_rows and n_cols must be at least 1.")
+        n_cells = n_rows * n_cols
+        if labels is not None and len(labels) != n_cells:
+            raise ValueError(
+                f"labels length ({len(labels)}) must match n_rows * n_cols ({n_cells})."
+            )
+
+        padded_x_min = x_min - padding
+        padded_x_max = x_max + padding
+        padded_y_min = y_min - padding
+        padded_y_max = y_max + padding
+
+        col_width = (padded_x_max - padded_x_min) / n_cols
+        row_height = (padded_y_max - padded_y_min) / n_rows
+
+        cells: List[GridCell] = []
+        index = 0
+        for row in range(n_rows):
+            for col in range(n_cols):
+                cell_x_min = padded_x_min + col * col_width
+                cell_x_max = padded_x_min + (col + 1) * col_width
+                cell_y_min = padded_y_max - (row + 1) * row_height
+                cell_y_max = padded_y_max - row * row_height
+                label = labels[index] if labels is not None else ""
+                cells.append(
+                    GridCell(
+                        x_min=cell_x_min,
+                        x_max=cell_x_max,
+                        y_min=cell_y_min,
+                        y_max=cell_y_max,
+                        index=index,
+                        label=label,
+                    )
+                )
+                index += 1
+
+        return cls(cells=cells)
+
+    def get_cell_for_point(self, x: float, y: float) -> int:
+        """Return the index of the cell containing the given point.
+
+        Iterates through cells and returns the index of the first cell whose
+        half-open interval [min, max) contains the point. Returns -1 if no
+        cell contains the point.
+
+        Args:
+            x: X coordinate of the point.
+            y: Y coordinate of the point.
+
+        Returns:
+            The index of the matching cell, or -1 if no cell contains the point.
+        """
+        for cell in self.cells:
+            if cell.x_min <= x < cell.x_max and cell.y_min <= y < cell.y_max:
+                return cell.index
+        return -1
+
+
 @dataclasses.dataclass
 class Stroke:
     """Represents a single stroke in an Alphabet or DSYM task.

src/graphomotor/utils/alphabet_utils.py

@@ -0,0 +1,65 @@
+"""Utility functions for Alphabet and DSYM stroke segmentation."""
+
+from typing import List, Optional
+
+import pandas as pd
+
+from graphomotor.core import models
+
+
+def segment_strokes(
+    data: pd.DataFrame,
+    x_min: float,
+    x_max: float,
+    y_min: float,
+    y_max: float,
+    n_rows: int,
+    n_cols: int,
+    labels: Optional[List[str]] = None,
+) -> models.Grid:
+    """Segment drawing data into strokes and assign them to grid cells.
+
+    Groups the data by line_number to create individual Stroke objects. Each
+    stroke is assigned to a GridCell based on its centroid (mean x, mean y).
+    The grid is constructed via Grid.from_bbox with default padding so that
+    centroids on the outermost edge are captured.
+
+    Args:
+        data: DataFrame containing drawing data with at least line_number,
+            x, y, and seconds columns.
+        x_min: Left boundary of the grid bounding box.
+        x_max: Right boundary of the grid bounding box.
+        y_min: Bottom boundary of the grid bounding box.
+        y_max: Top boundary of the grid bounding box.
+        n_rows: Number of rows in the grid.
+        n_cols: Number of columns in the grid.
+        labels: Optional list of labels for each cell in row-major order.
+            Must have length n_rows * n_cols if provided.
+
+    Returns:
+        A Grid populated with strokes assigned to their matching cells.
+    """
+    grid = models.Grid.from_bbox(
+        x_min=x_min,
+        x_max=x_max,
+        y_min=y_min,
+        y_max=y_max,
+        n_rows=n_rows,
+        n_cols=n_cols,
+        labels=labels,
+    )
+
+    for line_number, group in data.groupby("line_number"):
+        stroke = models.Stroke(
+            points=group.reset_index(drop=True),
+            line_number=int(line_number),
+        )
+
+        centroid_x = group["x"].mean()
+        centroid_y = group["y"].mean()
+        cell_index = grid.get_cell_for_point(centroid_x, centroid_y)
+
+        if cell_index != -1:
+            grid.cells[cell_index].strokes.append(stroke)
+
+    return grid

tests/unit/test_alphabet_utils.py

@@ -0,0 +1,182 @@
+"""Test cases for the segment_strokes utility function."""
+
+import pandas as pd
+
+from graphomotor.utils import alphabet_utils
+
+
+def _make_drawing_data() -> pd.DataFrame:
+    """Create drawing data with three strokes in distinct spatial regions.
+
+    Stroke 0 has centroid near (5, 85) - top-left of a 2x2 grid.
+    Stroke 1 has centroid near (55, 85) - top-right.
+    Stroke 2 has centroid near (5, 15) - bottom-left.
+    """
+    return pd.DataFrame(
+        {
+            "line_number": [0, 0, 0, 1, 1, 1, 2, 2, 2],
+            "x": [3.0, 5.0, 7.0, 53.0, 55.0, 57.0, 3.0, 5.0, 7.0],
+            "y": [83.0, 85.0, 87.0, 83.0, 85.0, 87.0, 13.0, 15.0, 17.0],
+            "seconds": [0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8],
+        }
+    )
+
+
+class TestSegmentStrokes:
+    """Tests for the segment_strokes function."""
+
+    def test_strokes_assigned_to_correct_cells(self) -> None:
+        """Each stroke should be placed in the cell containing its centroid."""
+        data = _make_drawing_data()
+        grid = alphabet_utils.segment_strokes(
+            data=data,
+            x_min=0.0,
+            x_max=100.0,
+            y_min=0.0,
+            y_max=100.0,
+            n_rows=2,
+            n_cols=2,
+            labels=["TL", "TR", "BL", "BR"],
+        )
+
+        assert len(grid.cells[0].strokes) == 1
+        assert grid.cells[0].strokes[0].line_number == 0
+        assert len(grid.cells[1].strokes) == 1
+        assert grid.cells[1].strokes[0].line_number == 1
+        assert len(grid.cells[2].strokes) == 1
+        assert grid.cells[2].strokes[0].line_number == 2
+        assert len(grid.cells[3].strokes) == 0
+
+    def test_total_stroke_count_matches_line_numbers(self) -> None:
+        """Total strokes across all cells should equal the number of line groups."""
+        data = _make_drawing_data()
+        grid = alphabet_utils.segment_strokes(
+            data=data,
+            x_min=0.0,
+            x_max=100.0,
+            y_min=0.0,
+            y_max=100.0,
+            n_rows=2,
+            n_cols=2,
+        )
+
+        total_strokes = sum(len(c.strokes) for c in grid.cells)
+        assert total_strokes == 3
+
+    def test_stroke_points_are_correct(self) -> None:
+        """Each Stroke should contain the correct subset of points."""
+        data = _make_drawing_data()
+        grid = alphabet_utils.segment_strokes(
+            data=data,
+            x_min=0.0,
+            x_max=100.0,
+            y_min=0.0,
+            y_max=100.0,
+            n_rows=2,
+            n_cols=2,
+        )
+
+        stroke_0 = grid.cells[0].strokes[0]
+        assert len(stroke_0.points) == 3
+        assert list(stroke_0.points["x"]) == [3.0, 5.0, 7.0]
+
+    def test_empty_dataframe(self) -> None:
+        """An empty DataFrame should produce a grid with no strokes."""
+        data = pd.DataFrame(columns=["line_number", "x", "y", "seconds"])
+        grid = alphabet_utils.segment_strokes(
+            data=data,
+            x_min=0.0,
+            x_max=10.0,
+            y_min=0.0,
+            y_max=10.0,
+            n_rows=1,
+            n_cols=1,
+        )
+
+        assert all(len(c.strokes) == 0 for c in grid.cells)
+
+    def test_stroke_outside_grid_is_not_assigned(self) -> None:
+        """Strokes whose centroids fall outside the grid should be dropped."""
+        data = pd.DataFrame(
+            {
+                "line_number": [0, 0],
+                "x": [500.0, 600.0],
+                "y": [500.0, 600.0],
+                "seconds": [0.0, 0.1],
+            }
+        )
+        grid = alphabet_utils.segment_strokes(
+            data=data,
+            x_min=0.0,
+            x_max=10.0,
+            y_min=0.0,
+            y_max=10.0,
+            n_rows=1,
+            n_cols=1,
+        )
+
+        assert len(grid.cells[0].strokes) == 0
+
+    def test_multiple_strokes_in_same_cell(self) -> None:
+        """Multiple strokes in the same spatial region should all land in one cell."""
+        data = pd.DataFrame(
+            {
+                "line_number": [0, 0, 1, 1, 2, 2],
+                "x": [5.0, 6.0, 5.5, 6.5, 4.5, 5.5],
+                "y": [5.0, 6.0, 5.5, 6.5, 4.5, 5.5],
+                "seconds": [0.0, 0.1, 0.2, 0.3, 0.4, 0.5],
+            }
+        )
+        grid = alphabet_utils.segment_strokes(
+            data=data,
+            x_min=0.0,
+            x_max=10.0,
+            y_min=0.0,
+            y_max=10.0,
+            n_rows=1,
+            n_cols=1,
+        )
+
+        assert len(grid.cells[0].strokes) == 3
+
+    def test_grid_structure_matches_parameters(self) -> None:
+        """Returned grid should have the correct number of labeled cells."""
+        data = _make_drawing_data()
+        labels = ["A", "B", "C", "D", "E", "F"]
+        grid = alphabet_utils.segment_strokes(
+            data=data,
+            x_min=0.0,
+            x_max=100.0,
+            y_min=0.0,
+            y_max=100.0,
+            n_rows=2,
+            n_cols=3,
+            labels=labels,
+        )
+
+        assert len(grid.cells) == 6
+        assert [c.label for c in grid.cells] == labels
+
+    def test_stroke_index_is_reset(self) -> None:
+        """Stroke points should have a reset index starting from 0."""
+        data = pd.DataFrame(
+            {
+                "line_number": [5, 5, 5],
+                "x": [1.0, 2.0, 3.0],
+                "y": [1.0, 2.0, 3.0],
+                "seconds": [0.0, 0.1, 0.2],
+            },
+            index=[10, 11, 12],
+        )
+        grid = alphabet_utils.segment_strokes(
+            data=data,
+            x_min=0.0,
+            x_max=10.0,
+            y_min=0.0,
+            y_max=10.0,
+            n_rows=1,
+            n_cols=1,
+        )
+
+        stroke = grid.cells[0].strokes[0]
+        assert list(stroke.points.index) == [0, 1, 2]