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#!/usr/bin/env python
# -*- coding: utf-8 -*-
# util.py
"""Several utility functions that don't really belong anywhere."""
# Copyright (c) 2009-2016 Aditya Panchal
# This file is part of dicompyler, released under a BSD license.
# See the file license.txt included with this distribution, also
# available at http://code.google.com/p/dicompyler/
import numpy as np
import collections
import sys
def piecewise(x, condlist, funclist, *args, **kw):
"""
Evaluate a piecewise-defined function.
(Borrowed from numpy 1.11 for compatibility for numpy 1.9-1.10)
Given a set of conditions and corresponding functions, evaluate each
function on the input data wherever its condition is true.
Parameters
----------
x : ndarray
The input domain.
condlist : list of bool arrays
Each boolean array corresponds to a function in `funclist`. Wherever
`condlist[i]` is True, `funclist[i](x)` is used as the output value.
Each boolean array in `condlist` selects a piece of `x`,
and should therefore be of the same shape as `x`.
The length of `condlist` must correspond to that of `funclist`.
If one extra function is given, i.e. if
``len(funclist) - len(condlist) == 1``, then that extra function
is the default value, used wherever all conditions are false.
funclist : list of callables, f(x,*args,**kw), or scalars
Each function is evaluated over `x` wherever its corresponding
condition is True. It should take an array as input and give an array
or a scalar value as output. If, instead of a callable,
a scalar is provided then a constant function (``lambda x: scalar``) is
assumed.
args : tuple, optional
Any further arguments given to `piecewise` are passed to the functions
upon execution, i.e., if called ``piecewise(..., ..., 1, 'a')``, then
each function is called as ``f(x, 1, 'a')``.
kw : dict, optional
Keyword arguments used in calling `piecewise` are passed to the
functions upon execution, i.e., if called
``piecewise(..., ..., lambda=1)``, then each function is called as
``f(x, lambda=1)``.
Returns
-------
out : ndarray
The output is the same shape and type as x and is found by
calling the functions in `funclist` on the appropriate portions of `x`,
as defined by the boolean arrays in `condlist`. Portions not covered
by any condition have a default value of 0.
See Also
--------
choose, select, where
Notes
-----
This is similar to choose or select, except that functions are
evaluated on elements of `x` that satisfy the corresponding condition from
`condlist`.
The result is::
|--
|funclist[0](x[condlist[0]])
out = |funclist[1](x[condlist[1]])
|...
|funclist[n2](x[condlist[n2]])
|--
Examples
--------
Define the sigma function, which is -1 for ``x < 0`` and +1 for ``x >= 0``.
>>> x = np.linspace(-2.5, 2.5, 6)
>>> np.piecewise(x, [x < 0, x >= 0], [-1, 1])
array([-1., -1., -1., 1., 1., 1.])
Define the absolute value, which is ``-x`` for ``x <0`` and ``x`` for
``x >= 0``.
>>> np.piecewise(x, [x < 0, x >= 0], [lambda x: -x, lambda x: x])
array([ 2.5, 1.5, 0.5, 0.5, 1.5, 2.5])
"""
# Use the built-in numpy piecewise function if not on numpy 1.9-1.10
version = np.version.version.split('.')
if (version[0] == '1') and (version[1] not in ['9', '10']):
return np.piecewise(x, condlist, funclist, *args, **kw)
x = np.asanyarray(x)
n2 = len(funclist)
if (np.isscalar(condlist) or not (isinstance(condlist[0], list) or
isinstance(condlist[0], np.ndarray))):
condlist = [condlist]
condlist = np.array(condlist, dtype=bool)
n = len(condlist)
# This is a hack to work around problems with NumPy's
# handling of 0-d arrays and boolean indexing with
# numpy.bool_ scalars
zerod = False
if x.ndim == 0:
x = x[None]
zerod = True
if condlist.shape[-1] != 1:
condlist = condlist.T
if n == n2 - 1: # compute the "otherwise" condition.
totlist = np.logical_or.reduce(condlist, axis=0)
# Only able to stack vertically if the array is 1d or less
if x.ndim <= 1:
condlist = np.vstack([condlist, ~totlist])
else:
condlist = [np.asarray(c, dtype=bool) for c in condlist]
totlist = condlist[0]
for k in range(1, n):
totlist |= condlist[k]
condlist.append(~totlist)
n += 1
y = np.zeros(x.shape, x.dtype)
for k in range(n):
item = funclist[k]
if not isinstance(item, collections.abc.Callable):
y[condlist[k]] = item
else:
vals = x[condlist[k]]
if vals.size > 0:
y[condlist[k]] = item(vals, *args, **kw)
if zerod:
y = y.squeeze()
return y
def platform():
if sys.platform.startswith('win'):
return 'windows'
elif sys.platform.startswith('darwin'):
return 'mac'
return 'linux'
|
