dask.array.rechunk

dask.array.rechunk(x, chunks='auto', threshold=None, block_size_limit=None, balance=False)[source]

Convert blocks in dask array x for new chunks.

Parameters
x: dask array

Array to be rechunked.

chunks: int, tuple, dict or str, optional

The new block dimensions to create. -1 indicates the full size of the corresponding dimension. Default is “auto” which automatically determines chunk sizes.

threshold: int, optional

The graph growth factor under which we don’t bother introducing an intermediate step.

block_size_limit: int, optional

The maximum block size (in bytes) we want to produce Defaults to the configuration value array.chunk-size

balancebool, default False

If True, try to make each chunk to be the same size.

This means balance=True will remove any small leftover chunks, so using x.rechunk(chunks=len(x) // N, balance=True) will almost certainly result in N chunks.

Examples

>>> import dask.array as da
>>> x = da.ones((1000, 1000), chunks=(100, 100))

Specify uniform chunk sizes with a tuple

>>> y = x.rechunk((1000, 10))

Or chunk only specific dimensions with a dictionary

>>> y = x.rechunk({0: 1000})

Use the value -1 to specify that you want a single chunk along a dimension or the value "auto" to specify that dask can freely rechunk a dimension to attain blocks of a uniform block size

>>> y = x.rechunk({0: -1, 1: 'auto'}, block_size_limit=1e8)

If a chunk size does not divide the dimension then rechunk will leave any unevenness to the last chunk.

>>> x.rechunk(chunks=(400, -1)).chunks
((400, 400, 200), (1000,))

However if you want more balanced chunks, and don’t mind Dask choosing a different chunksize for you then you can use the balance=True option.

>>> x.rechunk(chunks=(400, -1), balance=True).chunks
((500, 500), (1000,))