Utility to turn block-ID into equivalent slice

[jhamman]

Suppose I have a array block id (e.g. "0.0.0") and I want its equivalent slice on the full array. Does Zarr currently have a function to do this? I'm looking for something like this:

In [1]: block_id = '0.0.0'

In [2]: block_size = (10, 20, 30)

In [3]: def slice_axis(key, chunk_size):
   ...:     return slice(key * chunk_size, (key + 1) * chunk_size)
   ...:
   ...:
   ...: def get_indexers(key, chunks):
   ...:     ikeys = key.split(".")
   ...:     return tuple(slice_axis(int(i), c) for i, c in zip(ikeys, chunks))
   ...:

In [4]: get_indexers(block_id, block_size)
Out[4]: (slice(0, 10, None), slice(0, 20, None), slice(0, 30, None))

In [5]: import numpy as np

In [6]: data = np.random.random((100, 100, 100))

In [7]: slices = get_indexers(block_id, block_size)

In [8]: data[slices]

I recognize this is actually the inverse operation that Zarr takes when slicing a zarr array (usually we go from slice -> block_id).

[jakirkham]

Similar to issue ( #543 ).