Question

我需要制作快速numpy数组，在每行中生成具有不同范围的随机整数。

我的代码可以工作，但当我将向量数增加到300000时速度很慢：

import numpy as np
import random

population_size = 4
vectors_number = population_size * 3 

add_matrix = []
for i in range(0, int(vectors_number/population_size)):
    candidates = list(range(population_size*i, population_size*(i+1))) 
    random_index = random.sample(candidates, 4)
    add_matrix.append(random_index)

winning_matrix = np.row_stack(add_matrix)
print(winning_matrix)

每行从可变范围中选择4个随机数。

输出：

[[ 3  0  1  2]
 [ 4  6  7  5]
 [11  9  8 10]]

最好只使用numpy without loops创建该矩阵

Answer 1

在您的情况下，可以使用map和列表推导来压缩循环。

winning_matrix = np.vstack ([random.sample (candidate, d2) for candidate in map (lambda i: list(range(population_size*i, population_size*(i+1))), range(0, int(vectors_number/population_size)))])

输出：

array([[ 0,  1,  3,  2],
       [ 5,  6,  4,  7],
       [11, 10,  9,  8]])

这可以分解为

# This is your loop generating the arrays from where you are sampling
range_list = map (lambda i: list(range(population_size*i, population_size*(i+1))), range(0, int(vectors_number/population_size)))
# This does the generation of the matrix, using exactly following your method
winning_matrix = np.vstack ([random.sample (candidate, d2) for candidate in range_list])

如果生成具有不同范围的随机整数（而不是样本），则可以按照以下方法。

这样的事情

# Generating upper and lower bounds for each row.
pair_ranges = product (list (range (1, 5)), list (range (5, 9)))
d2 = 4
np.vstack ([np.random.random_integers (x, y, [1, d2]) for x, y in pair_ranges])

输出：

array([[2, 5, 2, 5],
       [5, 6, 2, 4],
       [1, 3, 2, 3],
       [4, 2, 4, 4],
       [2, 6, 4, 6],
       [7, 2, 6, 3],
       [4, 5, 3, 5],
       [4, 6, 3, 6],
       [3, 6, 3, 6]])

行将在范围

之间具有随机整数

array([[1, 5],
       [1, 6],
       [1, 7],
       [2, 5],
       [2, 6],
       [2, 7],
       [3, 5],
       [3, 6],
       [3, 7]])

Answer 2

这是this trick之后的矢量化方法，用于提取唯一的随机样本 -

ncols = 4
N = int(vectors_number/population_size)
offset = np.arange(N)[:,None]*population_size
winning_matrix = np.random.rand(N,population_size).argsort(1)[:,:ncols] + offset

我们还可以利用np.argpartition替换最后一步 -

r = np.random.rand(N,population_size)
out = r.argpartition(ncols,axis=1)[:,:ncols] + offset

计时 -

In [63]: import numpy as np
    ...: import random
    ...: 
    ...: population_size = 64
    ...: vectors_number = population_size * 300000

In [64]: %%timeit
    ...: add_matrix = []
    ...: for i in range(0, int(vectors_number/population_size)):
    ...:     candidates = list(range(population_size*i, population_size*(i+1))) 
    ...:     random_index = random.sample(candidates, 4)
    ...:     add_matrix.append(random_index)
    ...: 
    ...: winning_matrix = np.row_stack(add_matrix)
1 loop, best of 3: 1.82 s per loop

In [65]: %%timeit
    ...: ncols = 4
    ...: N = int(vectors_number/population_size)
    ...: offset = np.arange(N)[:,None]*population_size
    ...: out = np.random.rand(N,population_size).argsort(1)[:,:ncols] + offset
1 loop, best of 3: 718 ms per loop

In [66]: %%timeit
    ...: ncols = 4
    ...: N = int(vectors_number/population_size)
    ...: offset = np.arange(N)[:,None]*population_size
    ...: r = np.random.rand(N,population_size)
    ...: out = r.argpartition(ncols,axis=1)[:,:ncols] + offset
1 loop, best of 3: 428 ms per loop

Answer 3

由于我们仅从4中选择64，因此很少发生碰撞，因此我们可以随后进行更换和更正。

import numpy as np

def multiperm(y, x, factor=16, remap=False):
    draw = np.random.randint(0, factor*x, (y, x))
    idx = np.full((y, factor*x), -1, dtype=np.int8 if factor*x < 128 else int)
    yi, xi = np.ogrid[:y, :x]
    idx[yi, draw] = xi
    yd, xd = np.where(idx[yi, draw] != xi)
    while yd.size > 0:
        ndraw = np.random.randint(0, factor*x, yd.shape)
        draw[yd, xd] = ndraw
        good = idx[yd, ndraw] == -1
        idx[yd[good], ndraw[good]] = xd[good]
        good[good] = idx[yd[good], ndraw[good]] == xd[good]
        yd, xd = yd[~good], xd[~good]
    if remap:
        idx = np.zeros((y, factor*x), dtype=np.int8)
        idx[yi, draw] = 1
        idx[0, 0] -= 1
        return idx.ravel().cumsum().reshape(idx.shape)[yi, draw]
    else:
        return draw + factor*x*yi

from timeit import timeit

print(timeit("multiperm(300_000, 4)", globals=globals(), number=100)*10, 'ms')

# sanity checks
check = multiperm(300_000, 4)
print(np.all(np.arange(300_000) * 64 <= check.T) and np.all(np.arange(1, 300_001) * 64 > check.T))
print(len(set(check.ravel().tolist())) == check.size)

示例运行：

44.83660604993929 ms
True
True

Answer 4

以更好的理解重新审视这个问题，结果只需要64个人群中的第一个随机4个，我得出了这个答案。仍然有一个循环，但它是一个循环超过少量的必需列，它基本上交换了前4个（FINALIST）列和一个随机的其他列：

import numpy as np

PLAYERS   = 64      # per game
GAMES     = 300000
FINALISTS = 4       # we only want to know the first four

# every player in every game has a unique id
matrix = np.arange(PLAYERS * GAMES).reshape((GAMES, PLAYERS))

games  = np.arange(GAMES)
swaps  = np.random.randint(0, PLAYERS, size=(FINALISTS, GAMES))

for i in range(FINALISTS):
    # some trickey stuff to create tuples for indexing
    dst = tuple(np.vstack([ games, i * np.ones(GAMES, dtype=np.int) ]))
    src = tuple(np.vstack([ games, swaps[i] ]))
    # do the a swap for location i 
    matrix[dst], matrix[src] = matrix[src], matrix[dst]

winning_matrix = matrix[:,:FINALISTS]
print(winning_matrix)

Answer 5

为什么不这样：

range_1 = np.array([1,2,3,4]
range_2 = np.array([10,20,30,40]

第一行的值在[1,10]之间，第二行的值在[2,20]之间，依此类推。

np.transpose(np.random.randint(range_1,range_2,(4,4))) 

In [34]: np.transpose(np.random.randint(range_1,range_2,(4,4)))  
Out[34]: 
array([[ 2,  2,  6,  3],
       [ 9,  5, 13, 11],
       [ 3,  9, 14, 27],
       [22, 15, 22, 32]])

使用随机整数创建numpy数组，每行包含另一个范围

5 个答案: