A minimal implementation of chunked, compressed, N-dimensional arrays for Python.
Project description
A minimal implementation of chunked, compressed, N-dimensional arrays for Python.
Source code: https://github.com/alimanfoo/zarr
Download: https://pypi.python.org/pypi/zarr
Installation
Installation requires NumPy and Cython pre-installed. Currently only compatible with Python >= 3.4.
Install from PyPI:
$ pip install -U zarr
Install from GitHub:
$ pip install -U git+https://github.com/alimanfoo/zarr.git@master
Status
Experimental, proof-of-concept. This is alpha-quality software. Things may break, change or disappear without warning.
Bug reports and suggestions welcome.
Design goals
Chunking in multiple dimensions
Resize any dimension
Concurrent reads
Concurrent writes
Release the GIL during compression and decompression
Usage
Create an array:
>>> import numpy as np >>> import zarr >>> z = zarr.empty(shape=(10000, 1000), dtype='i4', chunks=(1000, 100)) >>> z zarr.ext.SynchronizedArray((10000, 1000), int32, chunks=(1000, 100)) cname: blosclz; clevel: 5; shuffle: 1 (BYTESHUFFLE) nbytes: 38.1M; cbytes: 0; initialized: 0/100
Fill it with some data:
>>> z[:] = np.arange(10000000, dtype='i4').reshape(10000, 1000) >>> z zarr.ext.SynchronizedArray((10000, 1000), int32, chunks=(1000, 100)) cname: blosclz; clevel: 5; shuffle: 1 (BYTESHUFFLE) nbytes: 38.1M; cbytes: 2.0M; ratio: 19.3; initialized: 100/100
Obtain a NumPy array by slicing:
>>> z[:] array([[ 0, 1, 2, ..., 997, 998, 999], [ 1000, 1001, 1002, ..., 1997, 1998, 1999], [ 2000, 2001, 2002, ..., 2997, 2998, 2999], ..., [9997000, 9997001, 9997002, ..., 9997997, 9997998, 9997999], [9998000, 9998001, 9998002, ..., 9998997, 9998998, 9998999], [9999000, 9999001, 9999002, ..., 9999997, 9999998, 9999999]], dtype=int32) >>> z[:100] array([[ 0, 1, 2, ..., 997, 998, 999], [ 1000, 1001, 1002, ..., 1997, 1998, 1999], [ 2000, 2001, 2002, ..., 2997, 2998, 2999], ..., [97000, 97001, 97002, ..., 97997, 97998, 97999], [98000, 98001, 98002, ..., 98997, 98998, 98999], [99000, 99001, 99002, ..., 99997, 99998, 99999]], dtype=int32) >>> z[:, :100] array([[ 0, 1, 2, ..., 97, 98, 99], [ 1000, 1001, 1002, ..., 1097, 1098, 1099], [ 2000, 2001, 2002, ..., 2097, 2098, 2099], ..., [9997000, 9997001, 9997002, ..., 9997097, 9997098, 9997099], [9998000, 9998001, 9998002, ..., 9998097, 9998098, 9998099], [9999000, 9999001, 9999002, ..., 9999097, 9999098, 9999099]], dtype=int32)
Resize the array and add more data:
>>> z.resize(20000, 1000) >>> z zarr.ext.SynchronizedArray((20000, 1000), int32, chunks=(1000, 100)) cname: blosclz; clevel: 5; shuffle: 1 (BYTESHUFFLE) nbytes: 76.3M; cbytes: 2.0M; ratio: 38.5; initialized: 100/200 >>> z[10000:, :] = np.arange(10000000, dtype='i4').reshape(10000, 1000) >>> z zarr.ext.SynchronizedArray((20000, 1000), int32, chunks=(1000, 100)) cname: blosclz; clevel: 5; shuffle: 1 (BYTESHUFFLE) nbytes: 76.3M; cbytes: 4.0M; ratio: 19.3; initialized: 200/200
For convenience, an append() method is also available, which can be used to append data to any axis:
>>> a = np.arange(10000000, dtype='i4').reshape(10000, 1000) >>> z = zarr.array(a, chunks=(1000, 100)) >>> z zarr.ext.SynchronizedArray((10000, 1000), int32, chunks=(1000, 100)) cname: blosclz; clevel: 5; shuffle: 1 (BYTESHUFFLE) nbytes: 38.1M; cbytes: 2.0M; ratio: 19.3; initialized: 100/100 >>> z.append(a+a) >>> z zarr.ext.SynchronizedArray((20000, 1000), int32, chunks=(1000, 100)) cname: blosclz; clevel: 5; shuffle: 1 (BYTESHUFFLE) nbytes: 76.3M; cbytes: 3.6M; ratio: 21.2; initialized: 200/200 >>> z.append(np.vstack([a, a]), axis=1) >>> z zarr.ext.SynchronizedArray((20000, 2000), int32, chunks=(1000, 100)) cname: blosclz; clevel: 5; shuffle: 1 (BYTESHUFFLE) nbytes: 152.6M; cbytes: 7.6M; ratio: 20.2; initialized: 400/400
Create a persistent array (data saved to disk):
>>> path = 'example.zarr' >>> z = zarr.open(path, shape=(10000, 1000), dtype='i4', chunks=(1000, 100)) >>> z[:] = np.arange(10000000, dtype='i4').reshape(10000, 1000) >>> z zarr.ext.SynchronizedPersistentArray((10000, 1000), int32, chunks=(1000, 100)) cname: blosclz; clevel: 5; shuffle: 1 (BYTESHUFFLE) nbytes: 38.1M; cbytes: 2.0M; ratio: 19.3; initialized: 100/100 mode: a; path: example.zarr
There is no need to close a persistent array. Data are automatically flushed to disk.
Tuning
zarr is designed for use in parallel computations working chunk-wise over data. Try it with dask.array.
zarr is optimised for accessing and storing data in contiguous slices, of the same size or larger than chunks. It is not and will never be optimised for single item access.
Chunks sizes >= 1M are generally good. Optimal chunk shape will depend on the correlation structure in your data.
Acknowledgments
zarr uses c-blosc internally for compression and decompression and borrows code heavily from bcolz.
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