a5_compaction: Compact and uncompact sets of cells

In a5R: 'A5' Discrete Global Grid System

Compact and uncompact sets of cells

Description

a5_compact() stores a set of cells as an a5_covering: every complete group of siblings is replaced by its parent, repeatedly, giving the fewest cells for the same set, and the covering records the resolution the set stands for. a5_uncompact() expands coverings back to their cells at that resolution, or at a finer one. Uncompacting a compacted set returns the original cells, sorted in curve order and without duplicates.

Usage

a5_compact(cell, resolution = NULL)

a5_uncompact(x, resolution = NULL, simplify = TRUE)

Arguments

cell	An a5_cell vector. NA cells are skipped.
resolution	Integer scalar resolution. For a5_compact(), the resolution the covering stands for: by default that of the finest cell, and never finer than it. For a5_uncompact(), the resolution to expand to: by default each covering's own, and never coarser than it.
x	An a5_covering vector, or an a5_cell vector treated as one covering (see as_a5_covering()).
simplify	Logical scalar. If TRUE (default), return one flat a5_cell vector with the cells of every covering concatenated in input order. If FALSE, return an a5_cell_list with one element per covering, suitable for a list column.

Details

Both work on the index hierarchy (see a5_hierarchy), so the coverage they preserve is the set of index descendants, not a geometric area.

Value

a5_compact(): an a5_covering of length one. a5_uncompact(): an a5_cell vector, or an a5_cell_list when simplify = FALSE, with each covering's cells in curve order. A missing covering contributes no cells (an empty element in the list form).

Memory

A covering can stand for far more cells than it stores: a country at resolution 18 is about a billion cells, stored as a few hundred thousand. a5_uncompact() refuses to build more than .Machine$integer.max cells; check with a5_covering printing first, and prefer the covering functions that work on compacted sets.

See Also

a5_covering, a5_polygon_to_cells() and a5_grid_disk(), which return coverings.

Examples

cell <- a5_lonlat_to_cell(-3.19, 55.95, resolution = 5)
children <- a5_cell_to_children(cell, child_resolution = 7)
covering <- a5_compact(children) # stored as the parent
covering
a5_uncompact(covering)           # the 16 children again

# expand to a finer resolution
a5_uncompact(a5_compact(cell), resolution = 7)

# one covering per element, kept apart with simplify = FALSE
disks <- a5_grid_disk(a5_cell_to_children(cell), k = 1)
a5_uncompact(disks, simplify = FALSE)

a5R documentation built on Oct. 19, 2026, 5:08 p.m.