Write a small example Zarr v2 store — altarr_example

Writes a zlib-compressed, C-order Zarr v2 array of doubles into dir and returns the path, ready for altarr_zarr_v2(). The store is made on demand rather than shipped, because Zarr v2 metadata files (.zarray) are hidden files, which R packages should not carry.

Usage

altarr_example_zarr(
  dir = tempfile("altarr-example-", fileext = ".zarr"),
  dim = c(70L, 50L, 30L),
  chunk = c(20L, 16L, 7L)
)

Arguments

dir: directory to write the store into (created if needed).
dim: R dimensions of the array (the Zarr shape is the reverse).
chunk: R chunk shape (the Zarr chunk shape is the reverse). Edge chunks are padded in the store, as Zarr requires.

Value

the store path, invisibly.

Details

Every value is its own 0-based position in R's column-major order, so a result can be checked by eye: in the array returned by altarr_zarr_v2(), element x[i, j, k] is (i - 1) + dim[1] * (j - 1) + dim[1] * dim[2] * (k - 1), and x[n] is n - 1.

Examples

path <- altarr_example_zarr()
x <- altarr_zarr_v2(path)
dim(x)
#> [1] 70 50 30
x[c(1, 2, 71)]   # 0, 1, 70
#> [1]  0  1 70