from __future__ import annotations
import builtins
import contextlib
import math
import warnings
from functools import partial
from itertools import product
from numbers import Integral
import numpy as np
from tlz import compose, get, partition_all
from dask import config
from dask.array.blockwise import blockwise
from dask.array.core import Array, _concatenate2, asanyarray, broadcast_to, handle_out
from dask.array.numpy_compat import ComplexWarning
from dask.array.utils import compute_meta, validate_axis
from dask.base import tokenize
from dask.blockwise import lol_tuples
from dask.highlevelgraph import HighLevelGraph
from dask.utils import funcname, getargspec, is_series_like
[docs]
def reduction(
x,
chunk,
aggregate,
axis=None,
keepdims=False,
dtype=None,
split_every=None,
combine=None,
name=None,
out=None,
concatenate=True,
output_size=1,
meta=None,
weights=None,
):
"""General version of reductions
Parameters
----------
x: Array
Data being reduced along one or more axes
chunk: callable(x_chunk, [weights_chunk=None], axis, keepdims)
First function to be executed when resolving the dask graph.
This function is applied in parallel to all original chunks of x.
See below for function parameters.
combine: callable(x_chunk, axis, keepdims), optional
Function used for intermediate recursive aggregation (see
split_every below). If omitted, it defaults to aggregate.
If the reduction can be performed in less than 3 steps, it will not
be invoked at all.
aggregate: callable(x_chunk, axis, keepdims)
Last function to be executed when resolving the dask graph,
producing the final output. It is always invoked, even when the reduced
Array counts a single chunk along the reduced axes.
axis: int or sequence of ints, optional
Axis or axes to aggregate upon. If omitted, aggregate along all axes.
keepdims: boolean, optional
Whether the reduction function should preserve the reduced axes,
leaving them at size ``output_size``, or remove them.
dtype: np.dtype
data type of output. This argument was previously optional, but
leaving as ``None`` will now raise an exception.
split_every: int >= 2 or dict(axis: int), optional
Determines the depth of the recursive aggregation. If set to or more
than the number of input chunks, the aggregation will be performed in
two steps, one ``chunk`` function per input chunk and a single
``aggregate`` function at the end. If set to less than that, an
intermediate ``combine`` function will be used, so that any one
``combine`` or ``aggregate`` function has no more than ``split_every``
inputs. The depth of the aggregation graph will be
:math:`log_{split_every}(input chunks along reduced axes)`. Setting to
a low value can reduce cache size and network transfers, at the cost of
more CPU and a larger dask graph.
Omit to let dask heuristically decide a good default. A default can
also be set globally with the ``split_every`` key in
:mod:`dask.config`.
name: str, optional
Prefix of the keys of the intermediate and output nodes. If omitted it
defaults to the function names.
out: Array, optional
Another dask array whose contents will be replaced. Omit to create a
new one. Note that, unlike in numpy, this setting gives no performance
benefits whatsoever, but can still be useful if one needs to preserve
the references to a previously existing Array.
concatenate: bool, optional
If True (the default), the outputs of the ``chunk``/``combine``
functions are concatenated into a single np.array before being passed
to the ``combine``/``aggregate`` functions. If False, the input of
``combine`` and ``aggregate`` will be either a list of the raw outputs
of the previous step or a single output, and the function will have to
concatenate it itself. It can be useful to set this to False if the
chunk and/or combine steps do not produce np.arrays.
output_size: int >= 1, optional
Size of the output of the ``aggregate`` function along the reduced
axes. Ignored if keepdims is False.
weights : array_like, optional
Weights to be used in the reduction of `x`. Will be
automatically broadcast to the shape of `x`, and so must have
a compatible shape. For instance, if `x` has shape ``(3, 4)``
then acceptable shapes for `weights` are ``(3, 4)``, ``(4,)``,
``(3, 1)``, ``(1, 1)``, ``(1)``, and ``()``.
Returns
-------
dask array
**Function Parameters**
x_chunk: numpy.ndarray
Individual input chunk. For ``chunk`` functions, it is one of the
original chunks of x. For ``combine`` and ``aggregate`` functions, it's
the concatenation of the outputs produced by the previous ``chunk`` or
``combine`` functions. If concatenate=False, it's a list of the raw
outputs from the previous functions.
weights_chunk: numpy.ndarray, optional
Only applicable to the ``chunk`` function. Weights, with the
same shape as `x_chunk`, to be applied during the reduction of
the individual input chunk. If ``weights`` have not been
provided then the function may omit this parameter. When
`weights_chunk` is included then it must occur immediately
after the `x_chunk` parameter, and must also have a default
value for cases when ``weights`` are not provided.
axis: tuple
Normalized list of axes to reduce upon, e.g. ``(0, )``
Scalar, negative, and None axes have been normalized away.
Note that some numpy reduction functions cannot reduce along multiple
axes at once and strictly require an int in input. Such functions have
to be wrapped to cope.
keepdims: bool
Whether the reduction function should preserve the reduced axes or
remove them.
"""
if axis is None:
axis = tuple(range(x.ndim))
if isinstance(axis, Integral):
axis = (axis,)
axis = validate_axis(axis, x.ndim)
if dtype is None:
raise ValueError("Must specify dtype")
if "dtype" in getargspec(chunk).args:
chunk = partial(chunk, dtype=dtype)
if "dtype" in getargspec(aggregate).args:
aggregate = partial(aggregate, dtype=dtype)
if is_series_like(x):
x = x.values
# Map chunk across all blocks
inds = tuple(range(x.ndim))
args = (x, inds)
if weights is not None:
# Broadcast weights to x and add to args
wgt = asanyarray(weights)
try:
wgt = broadcast_to(wgt, x.shape)
except ValueError:
raise ValueError(
f"Weights with shape {wgt.shape} are not broadcastable "
f"to x with shape {x.shape}"
)
args += (wgt, inds)
# The dtype of `tmp` doesn't actually matter, and may be incorrect.
tmp = blockwise(
chunk, inds, *args, axis=axis, keepdims=True, token=name, dtype=dtype or float
)
tmp._chunks = tuple(
(output_size,) * len(c) if i in axis else c for i, c in enumerate(tmp.chunks)
)
if meta is None and hasattr(x, "_meta"):
try:
reduced_meta = compute_meta(
chunk, x.dtype, x._meta, axis=axis, keepdims=True, computing_meta=True
)
except TypeError:
reduced_meta = compute_meta(
chunk, x.dtype, x._meta, axis=axis, keepdims=True
)
except ValueError:
pass
else:
reduced_meta = None
result = _tree_reduce(
tmp,
aggregate,
axis,
keepdims,
dtype,
split_every,
combine,
name=name,
concatenate=concatenate,
reduced_meta=reduced_meta,
)
if keepdims and output_size != 1:
result._chunks = tuple(
(output_size,) if i in axis else c for i, c in enumerate(tmp.chunks)
)
if meta is not None:
result._meta = meta
return handle_out(out, result)
def _tree_reduce(
x,
aggregate,
axis,
keepdims,
dtype,
split_every=None,
combine=None,
name=None,
concatenate=True,
reduced_meta=None,
):
"""Perform the tree reduction step of a reduction.
Lower level, users should use ``reduction`` or ``arg_reduction`` directly.
"""
# Normalize split_every
split_every = split_every or config.get("split_every", 4)
if isinstance(split_every, dict):
split_every = {k: split_every.get(k, 2) for k in axis}
elif isinstance(split_every, Integral):
n = builtins.max(int(split_every ** (1 / (len(axis) or 1))), 2)
split_every = dict.fromkeys(axis, n)
else:
raise ValueError("split_every must be a int or a dict")
# Reduce across intermediates
depth = 1
for i, n in enumerate(x.numblocks):
if i in split_every and split_every[i] != 1:
depth = int(builtins.max(depth, math.ceil(math.log(n, split_every[i]))))
func = partial(combine or aggregate, axis=axis, keepdims=True)
if concatenate:
func = compose(func, partial(_concatenate2, axes=sorted(axis)))
for _ in range(depth - 1):
x = partial_reduce(
func,
x,
split_every,
True,
dtype=dtype,
name=(name or funcname(combine or aggregate)) + "-partial",
reduced_meta=reduced_meta,
)
func = partial(aggregate, axis=axis, keepdims=keepdims)
if concatenate:
func = compose(func, partial(_concatenate2, axes=sorted(axis)))
return partial_reduce(
func,
x,
split_every,
keepdims=keepdims,
dtype=dtype,
name=(name or funcname(aggregate)) + "-aggregate",
reduced_meta=reduced_meta,
)
def partial_reduce(
func, x, split_every, keepdims=False, dtype=None, name=None, reduced_meta=None
):
"""Partial reduction across multiple axes.
Parameters
----------
func : function
x : Array
split_every : dict
Maximum reduction block sizes in each dimension.
Examples
--------
Reduce across axis 0 and 2, merging a maximum of 1 block in the 0th
dimension, and 3 blocks in the 2nd dimension:
>>> partial_reduce(np.min, x, {0: 1, 2: 3}) # doctest: +SKIP
"""
name = (
(name or funcname(func)) + "-" + tokenize(func, x, split_every, keepdims, dtype)
)
parts = [
list(partition_all(split_every.get(i, 1), range(n)))
for (i, n) in enumerate(x.numblocks)
]
keys = product(*map(range, map(len, parts)))
out_chunks = [
tuple(1 for p in partition_all(split_every[i], c)) if i in split_every else c
for (i, c) in enumerate(x.chunks)
]
if not keepdims:
out_axis = [i for i in range(x.ndim) if i not in split_every]
getter = lambda k: get(out_axis, k)
keys = map(getter, keys)
out_chunks = list(getter(out_chunks))
dsk = {}
for k, p in zip(keys, product(*parts)):
free = {
i: j[0] for (i, j) in enumerate(p) if len(j) == 1 and i not in split_every
}
dummy = dict(i for i in enumerate(p) if i[0] in split_every)
g = lol_tuples((x.name,), range(x.ndim), free, dummy)
dsk[(name,) + k] = (func, g)
graph = HighLevelGraph.from_collections(name, dsk, dependencies=[x])
meta = x._meta
if reduced_meta is not None:
try:
meta = func(reduced_meta, computing_meta=True)
# no meta keyword argument exists for func, and it isn't required
except TypeError:
try:
meta = func(reduced_meta)
except ValueError as e:
# min/max functions have no identity, don't apply function to meta
if "zero-size array to reduction operation" in str(e):
meta = reduced_meta
# when no work can be computed on the empty array (e.g., func is a ufunc)
except ValueError:
pass
if np.isscalar(meta):
return Array(graph, name, out_chunks, dtype=dtype)
else:
with contextlib.suppress(AttributeError), warnings.catch_warnings():
if name.startswith(("var", "moment")):
warnings.simplefilter("ignore", ComplexWarning)
meta = meta.astype(dtype)
return Array(graph, name, out_chunks, meta=meta)
