numpy fromiter与列表生成器 [英] numpy fromiter with generator of list

问题描述

import numpy as np
def gen_c():
    c = np.ones(5, dtype=int)
    j = 0
    t = 10
    while j < t:
        c[0] = j
        yield c.tolist()
        j += 1 

# What I did:
# res = np.array(list(gen_c())) <-- useless allocation of memory

# this line is what I'd like to do and it's killing me
res = np.fromiter(gen_c(), dtype=int) # dtype=list ?

错误提示ValueError: setting an array element with a sequence.

这是一段非常愚蠢的代码.我想从生成器创建一个列表数组(最终是2D数组)...

This is a very stupid piece of code. I'd like to create an array of list(finally a 2D array) from a generator...

尽管我到处搜索，但仍然无法弄清楚它如何工作.

Although I searched everywhere, I still cannot figure out how to make it work.

推荐答案

您只能使用 numpy.fromiter() 来创建一维数组(而不是二维数组)，如

You can only use numpy.fromiter() to create 1-dimensional arrays (not 2-D arrays) as given in the documentation of numpy.fromiter -

numpy.fromiter(iterable，dtype，count = -1)

从可迭代对象创建新的一维数组.

Create a new 1-dimensional array from an iterable object.

您可以做的一件事是转换生成器函数以从c中给出单个值，然后从中创建一个一维数组，然后将其重塑为(-1,5).示例-

One thing you can do is convert your generator function to give out single values from c and then create a 1D array from it and then reshape it to (-1,5) . Example -

import numpy as np
def gen_c():
    c = np.ones(5, dtype=int)
    j = 0
    t = 10
    while j < t:
        c[0] = j
        for i in c:
            yield i
        j += 1

np.fromiter(gen_c(),dtype=int).reshape((-1,5))

演示-

In [5]: %paste
import numpy as np
def gen_c():
    c = np.ones(5, dtype=int)
    j = 0
    t = 10
    while j < t:
        c[0] = j
        for i in c:
            yield i
        j += 1

np.fromiter(gen_c(),dtype=int).reshape((-1,5))

## -- End pasted text --
Out[5]:
array([[0, 1, 1, 1, 1],
       [1, 1, 1, 1, 1],
       [2, 1, 1, 1, 1],
       [3, 1, 1, 1, 1],
       [4, 1, 1, 1, 1],
       [5, 1, 1, 1, 1],
       [6, 1, 1, 1, 1],
       [7, 1, 1, 1, 1],
       [8, 1, 1, 1, 1],
       [9, 1, 1, 1, 1]])

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