Add hexagon backend

pipeline/sources/postcodes.py

@@ -0,0 +1,48 @@
+from pathlib import Path
+import polars as pl
+import h3
+
+from pipeline.config import DATA_DIR, H3_RESOLUTIONS, PROCESSED_DIR
+
+
+def lat_long_to_h3(lat: float, long: float, resolution: int) -> str:
+    """Convert lat/long to H3 index at given resolution."""
+    return h3.latlng_to_cell(lat, long, resolution)
+
+
+def load_postcodes() -> pl.LazyFrame:
+    """Load postcode data from arcgis parquet file."""
+    return pl.scan_parquet(DATA_DIR / "arcgis_data.parquet").select(
+        pl.col("pcds").alias("postcode"),
+        pl.col("lat"),
+        pl.col("long"),
+    )
+
+
+def process_postcodes() -> pl.LazyFrame:
+    """Process postcodes and add H3 indices at multiple resolutions."""
+    df = load_postcodes().collect()
+
+    for res in H3_RESOLUTIONS:
+        col_name = f"h3_res{res}"
+        df = df.with_columns(
+            pl.struct(["lat", "long"])
+            .map_elements(
+                lambda x: lat_long_to_h3(x["lat"], x["long"], res),
+                return_dtype=pl.Utf8,
+            )
+            .alias(col_name)
+        )
+
+    return df.lazy()
+
+
+def save_postcodes(output_path: Path | None = None) -> Path:
+    """Process and save postcodes with H3 indices."""
+    output_path = output_path or PROCESSED_DIR / "postcodes_h3.parquet"
+    output_path.parent.mkdir(parents=True, exist_ok=True)
+
+    df = process_postcodes().collect()
+    df.write_parquet(output_path)
+
+    return output_path