# Author: Hamzeh Alsalhi <ha258@cornell.edu>
#
# License: BSD 3 clause
from __future__ import division
import numpy as np
import scipy.sparse as sp
import operator
import array
from sklearn.utils import check_random_state
from sklearn.utils.fixes import astype
from ._random import sample_without_replacement
__all__ = ['sample_without_replacement', 'choice']
# This is a backport of np.random.choice from numpy 1.7
# The function can be removed when we bump the requirements to >=1.7
def choice(a, size=None, replace=True, p=None, random_state=None):
"""
choice(a, size=None, replace=True, p=None)
Generates a random sample from a given 1-D array
.. versionadded:: 1.7.0
Parameters
-----------
a : 1-D array-like or int
If an ndarray, a random sample is generated from its elements.
If an int, the random sample is generated as if a was np.arange(n)
size : int or tuple of ints, optional
Output shape. Default is None, in which case a single value is
returned.
replace : boolean, optional
Whether the sample is with or without replacement.
p : 1-D array-like, optional
The probabilities associated with each entry in a.
If not given the sample assumes a uniform distribution over all
entries in a.
random_state : int, RandomState instance or None, optional (default=None)
If int, random_state is the seed used by the random number generator;
If RandomState instance, random_state is the random number generator;
If None, the random number generator is the RandomState instance used
by `np.random`.
Returns
--------
samples : 1-D ndarray, shape (size,)
The generated random samples
Raises
-------
ValueError
If a is an int and less than zero, if a or p are not 1-dimensional,
if a is an array-like of size 0, if p is not a vector of
probabilities, if a and p have different lengths, or if
replace=False and the sample size is greater than the population
size
See Also
---------
randint, shuffle, permutation
Examples
---------
Generate a uniform random sample from np.arange(5) of size 3:
>>> np.random.choice(5, 3) # doctest: +SKIP
array([0, 3, 4])
>>> #This is equivalent to np.random.randint(0,5,3)
Generate a non-uniform random sample from np.arange(5) of size 3:
>>> np.random.choice(5, 3, p=[0.1, 0, 0.3, 0.6, 0]) # doctest: +SKIP
array([3, 3, 0])
Generate a uniform random sample from np.arange(5) of size 3 without
replacement:
>>> np.random.choice(5, 3, replace=False) # doctest: +SKIP
array([3,1,0])
>>> #This is equivalent to np.random.shuffle(np.arange(5))[:3]
Generate a non-uniform random sample from np.arange(5) of size
3 without replacement:
>>> np.random.choice(5, 3, replace=False, p=[0.1, 0, 0.3, 0.6, 0])
... # doctest: +SKIP
array([2, 3, 0])
Any of the above can be repeated with an arbitrary array-like
instead of just integers. For instance:
>>> aa_milne_arr = ['pooh', 'rabbit', 'piglet', 'Christopher']
>>> np.random.choice(aa_milne_arr, 5, p=[0.5, 0.1, 0.1, 0.3])
... # doctest: +SKIP
array(['pooh', 'pooh', 'pooh', 'Christopher', 'piglet'],
dtype='|S11')
"""
random_state = check_random_state(random_state)
# Format and Verify input
a = np.array(a, copy=False)
if a.ndim == 0:
try:
# __index__ must return an integer by python rules.
pop_size = operator.index(a.item())
except TypeError:
raise ValueError("a must be 1-dimensional or an integer")
if pop_size <= 0:
raise ValueError("a must be greater than 0")
elif a.ndim != 1:
raise ValueError("a must be 1-dimensional")
else:
pop_size = a.shape[0]
if pop_size is 0:
raise ValueError("a must be non-empty")
if p is not None:
p = np.array(p, dtype=np.double, ndmin=1, copy=False)
if p.ndim != 1:
raise ValueError("p must be 1-dimensional")
if p.size != pop_size:
raise ValueError("a and p must have same size")
if np.any(p < 0):
raise ValueError("probabilities are not non-negative")
if not np.allclose(p.sum(), 1):
raise ValueError("probabilities do not sum to 1")
shape = size
if shape is not None:
size = np.prod(shape, dtype=np.intp)
else:
size = 1
# Actual sampling
if replace:
if p is not None:
cdf = p.cumsum()
cdf /= cdf[-1]
uniform_samples = random_state.random_sample(shape)
idx = cdf.searchsorted(uniform_samples, side='right')
# searchsorted returns a scalar
idx = np.array(idx, copy=False)
else:
idx = random_state.randint(0, pop_size, size=shape)
else:
if size > pop_size:
raise ValueError("Cannot take a larger sample than "
"population when 'replace=False'")
if p is not None:
if np.sum(p > 0) < size:
raise ValueError("Fewer non-zero entries in p than size")
n_uniq = 0
p = p.copy()
found = np.zeros(shape, dtype=np.int)
flat_found = found.ravel()
while n_uniq < size:
x = random_state.rand(size - n_uniq)
if n_uniq > 0:
p[flat_found[0:n_uniq]] = 0
cdf = np.cumsum(p)
cdf /= cdf[-1]
new = cdf.searchsorted(x, side='right')
_, unique_indices = np.unique(new, return_index=True)
unique_indices.sort()
new = new.take(unique_indices)
flat_found[n_uniq:n_uniq + new.size] = new
n_uniq += new.size
idx = found
else:
idx = random_state.permutation(pop_size)[:size]
if shape is not None:
idx.shape = shape
if shape is None and isinstance(idx, np.ndarray):
# In most cases a scalar will have been made an array
idx = idx.item(0)
# Use samples as indices for a if a is array-like
if a.ndim == 0:
return idx
if shape is not None and idx.ndim == 0:
# If size == () then the user requested a 0-d array as opposed to
# a scalar object when size is None. However a[idx] is always a
# scalar and not an array. So this makes sure the result is an
# array, taking into account that np.array(item) may not work
# for object arrays.
res = np.empty((), dtype=a.dtype)
res[()] = a[idx]
return res
return a[idx]
def random_choice_csc(n_samples, classes, class_probability=None,
random_state=None):
"""Generate a sparse random matrix given column class distributions
Parameters
----------
n_samples : int,
Number of samples to draw in each column.
classes : list of size n_outputs of arrays of size (n_classes,)
List of classes for each column.
class_probability : list of size n_outputs of arrays of size (n_classes,)
Optional (default=None). Class distribution of each column. If None the
uniform distribution is assumed.
random_state : int, RandomState instance or None, optional (default=None)
If int, random_state is the seed used by the random number generator;
If RandomState instance, random_state is the random number generator;
If None, the random number generator is the RandomState instance used
by `np.random`.
Returns
-------
random_matrix : sparse csc matrix of size (n_samples, n_outputs)
"""
data = array.array('i')
indices = array.array('i')
indptr = array.array('i', [0])
for j in range(len(classes)):
classes[j] = np.asarray(classes[j])
if classes[j].dtype.kind != 'i':
raise ValueError("class dtype %s is not supported" %
classes[j].dtype)
classes[j] = astype(classes[j], np.int64, copy=False)
# use uniform distribution if no class_probability is given
if class_probability is None:
class_prob_j = np.empty(shape=classes[j].shape[0])
class_prob_j.fill(1 / classes[j].shape[0])
else:
class_prob_j = np.asarray(class_probability[j])
if np.sum(class_prob_j) != 1.0:
raise ValueError("Probability array at index {0} does not sum to "
"one".format(j))
if class_prob_j.shape[0] != classes[j].shape[0]:
raise ValueError("classes[{0}] (length {1}) and "
"class_probability[{0}] (length {2}) have "
"different length.".format(j,
classes[j].shape[0],
class_prob_j.shape[0]))
# If 0 is not present in the classes insert it with a probability 0.0
if 0 not in classes[j]:
classes[j] = np.insert(classes[j], 0, 0)
class_prob_j = np.insert(class_prob_j, 0, 0.0)
# If there are nonzero classes choose randomly using class_probability
rng = check_random_state(random_state)
if classes[j].shape[0] > 1:
p_nonzero = 1 - class_prob_j[classes[j] == 0]
nnz = int(n_samples * p_nonzero)
ind_sample = sample_without_replacement(n_population=n_samples,
n_samples=nnz,
random_state=random_state)
indices.extend(ind_sample)
# Normalize probabilites for the nonzero elements
classes_j_nonzero = classes[j] != 0
class_probability_nz = class_prob_j[classes_j_nonzero]
class_probability_nz_norm = (class_probability_nz /
np.sum(class_probability_nz))
classes_ind = np.searchsorted(class_probability_nz_norm.cumsum(),
rng.rand(nnz))
data.extend(classes[j][classes_j_nonzero][classes_ind])
indptr.append(len(indices))
return sp.csc_matrix((data, indices, indptr),
(n_samples, len(classes)),
dtype=int)