1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
|
"""
Utilities that manipulate strides to achieve desirable effects.
An explanation of strides can be found in the "ndarray.rst" file in the
NumPy reference guide.
"""
from __future__ import division, absolute_import, print_function
import numpy as np
__all__ = ['broadcast_to', 'broadcast_arrays']
class DummyArray(object):
"""Dummy object that just exists to hang __array_interface__ dictionaries
and possibly keep alive a reference to a base array.
"""
def __init__(self, interface, base=None):
self.__array_interface__ = interface
self.base = base
def _maybe_view_as_subclass(original_array, new_array):
if type(original_array) is not type(new_array):
# if input was an ndarray subclass and subclasses were OK,
# then view the result as that subclass.
new_array = new_array.view(type=type(original_array))
# Since we have done something akin to a view from original_array, we
# should let the subclass finalize (if it has it implemented, i.e., is
# not None).
if new_array.__array_finalize__:
new_array.__array_finalize__(original_array)
return new_array
def as_strided(x, shape=None, strides=None, subok=False):
""" Make an ndarray from the given array with the given shape and strides.
"""
# first convert input to array, possibly keeping subclass
x = np.array(x, copy=False, subok=subok)
interface = dict(x.__array_interface__)
if shape is not None:
interface['shape'] = tuple(shape)
if strides is not None:
interface['strides'] = tuple(strides)
array = np.asarray(DummyArray(interface, base=x))
if array.dtype.fields is None and x.dtype.fields is not None:
# This should only happen if x.dtype is [('', 'Vx')]
array.dtype = x.dtype
return _maybe_view_as_subclass(x, array)
def _broadcast_to(array, shape, subok, readonly):
shape = tuple(shape) if np.iterable(shape) else (shape,)
array = np.array(array, copy=False, subok=subok)
if not shape and array.shape:
raise ValueError('cannot broadcast a non-scalar to a scalar array')
if any(size < 0 for size in shape):
raise ValueError('all elements of broadcast shape must be non-'
'negative')
needs_writeable = not readonly and array.flags.writeable
extras = ['reduce_ok'] if needs_writeable else []
op_flag = 'readwrite' if needs_writeable else 'readonly'
broadcast = np.nditer(
(array,), flags=['multi_index', 'refs_ok', 'zerosize_ok'] + extras,
op_flags=[op_flag], itershape=shape, order='C').itviews[0]
result = _maybe_view_as_subclass(array, broadcast)
if needs_writeable and not result.flags.writeable:
result.flags.writeable = True
return result
def broadcast_to(array, shape, subok=False):
"""Broadcast an array to a new shape.
Parameters
----------
array : array_like
The array to broadcast.
shape : tuple
The shape of the desired array.
subok : bool, optional
If True, then sub-classes will be passed-through, otherwise
the returned array will be forced to be a base-class array (default).
Returns
-------
broadcast : array
A readonly view on the original array with the given shape. It is
typically not contiguous. Furthermore, more than one element of a
broadcasted array may refer to a single memory location.
Raises
------
ValueError
If the array is not compatible with the new shape according to NumPy's
broadcasting rules.
Notes
-----
.. versionadded:: 1.10.0
Examples
--------
>>> x = np.array([1, 2, 3])
>>> np.broadcast_to(x, (3, 3))
array([[1, 2, 3],
[1, 2, 3],
[1, 2, 3]])
"""
return _broadcast_to(array, shape, subok=subok, readonly=True)
def _broadcast_shape(*args):
"""Returns the shape of the ararys that would result from broadcasting the
supplied arrays against each other.
"""
if not args:
raise ValueError('must provide at least one argument')
# use the old-iterator because np.nditer does not handle size 0 arrays
# consistently
b = np.broadcast(*args[:32])
# unfortunately, it cannot handle 32 or more arguments directly
for pos in range(32, len(args), 31):
# ironically, np.broadcast does not properly handle np.broadcast
# objects (it treats them as scalars)
# use broadcasting to avoid allocating the full array
b = broadcast_to(0, b.shape)
b = np.broadcast(b, *args[pos:(pos + 31)])
return b.shape
def broadcast_arrays(*args, **kwargs):
"""
Broadcast any number of arrays against each other.
Parameters
----------
`*args` : array_likes
The arrays to broadcast.
subok : bool, optional
If True, then sub-classes will be passed-through, otherwise
the returned arrays will be forced to be a base-class array (default).
Returns
-------
broadcasted : list of arrays
These arrays are views on the original arrays. They are typically
not contiguous. Furthermore, more than one element of a
broadcasted array may refer to a single memory location. If you
need to write to the arrays, make copies first.
Examples
--------
>>> x = np.array([[1,2,3]])
>>> y = np.array([[1],[2],[3]])
>>> np.broadcast_arrays(x, y)
[array([[1, 2, 3],
[1, 2, 3],
[1, 2, 3]]), array([[1, 1, 1],
[2, 2, 2],
[3, 3, 3]])]
Here is a useful idiom for getting contiguous copies instead of
non-contiguous views.
>>> [np.array(a) for a in np.broadcast_arrays(x, y)]
[array([[1, 2, 3],
[1, 2, 3],
[1, 2, 3]]), array([[1, 1, 1],
[2, 2, 2],
[3, 3, 3]])]
"""
# nditer is not used here to avoid the limit of 32 arrays.
# Otherwise, something like the following one-liner would suffice:
# return np.nditer(args, flags=['multi_index', 'zerosize_ok'],
# order='C').itviews
subok = kwargs.pop('subok', False)
if kwargs:
raise TypeError('broadcast_arrays() got an unexpected keyword '
'argument {}'.format(kwargs.pop()))
args = [np.array(_m, copy=False, subok=subok) for _m in args]
shape = _broadcast_shape(*args)
if all(array.shape == shape for array in args):
# Common case where nothing needs to be broadcasted.
return args
# TODO: consider making the results of broadcast_arrays readonly to match
# broadcast_to. This will require a deprecation cycle.
return [_broadcast_to(array, shape, subok=subok, readonly=False)
for array in args]
|
