byCoordinate

import mir.array.allocation: array;
import mir.ndslice.sorting: sort;

auto slice = sparse!double(3, 3);
slice[] = [[0, 2, 1], [0, 0, 4], [6, 7, 0]];
assert(slice.byCoordinate.array.sort() == [
    [0, 1],
    [0, 2],
    [1, 2],
    [2, 0],
    [2, 1]]);