Function sparse_to_dense

nodedb-array/src/tile/promotion.rs:37–77

Convert a sparse tile to a dense tile by materialising every cell. Cells absent in the sparse payload become [`CellValue::Null`]. The caller is responsible for the integer-only-dim precondition (dense indexing relies on integer cell offsets) — this is enforced because non-`Int64`/`TimestampMs` dims do not have well-defined `tile_extent` semantics in dense layout.

(tile: &SparseTile, schema: &ArraySchema)

/// because non-`Int64`/`TimestampMs` dims do not have well-defined
/// `tile_extent` semantics in dense layout.
pub fn sparse_to_dense(tile: &SparseTile, schema: &ArraySchema) -> ArrayResult<DenseTile> {
    use crate::schema::dim_spec::DimType;
    use crate::types::coord::value::CoordValue;
    for d in &schema.dims {
        if !matches!(d.dtype, DimType::Int64 | DimType::TimestampMs) {
            return Err(ArrayError::InvalidSchema {
                array: schema.name.clone(),
                detail: format!(
                    "dense promotion requires integer dims; '{}' is {:?}",
                    d.name, d.dtype
                ),
            });
        }
    }
    let mut dense = DenseTile::empty(schema);
    let mut mbr = MbrBuilder::new(schema.arity(), schema.attrs.len());
    let n_rows = tile.nnz() as usize;
    for row in 0..n_rows {
        // Reconstruct row's coord from the dim dictionaries.
        let coord: Vec<CoordValue> = schema
            .dims
            .iter()
            .enumerate()
            .map(|(i, _)| {
                let dict = &tile.dim_dicts[i];
                let idx = dict.indices[row] as usize;
                dict.values[idx].clone()
            })
            .collect();
        let attrs: Vec<CellValue> = (0..schema.attrs.len())
            .map(|i| tile.attr_cols[i][row].clone())
            .collect();
        let flat = flat_index_for_coord(schema, &coord)?;
        for (i, a) in attrs.iter().enumerate() {
            dense.attr_cols[i][flat] = a.clone();
        }
        mbr.fold(&coord, &attrs);
    }
    dense.mbr = mbr.build();
    Ok(dense)
}

/// Row-major flat index `((c0 - lo0) * extent1 * extent2 ...) + ...`.
fn flat_index_for_coord(