python - 如何将包含嵌套数组的压缩对象展平到列表中？

Question

我有一个像这样的压缩对象:

z = zip(a, b)
lst = list(z)

print(lst)

输出:

[(0, array([[72, 65],
           [70, 71]], dtype=uint8)), 
(1, array([[ 71,  99],
           [190, 163]], dtype=uint8)), 
(2, array([[52, 59],
           [69, 72]], dtype=uint8)), etc...

我想将此列表展平为以下内容:

[0, 72, 65, 70, 71, 1, 71, 99, 190, 163, 2, 52, 59 etc..]

我试过用

y = sum(w, ())
# or 
y = list(itertools.chain(*lst))

但是当我打印时数组仍然存在。

我做错了什么？

Answer 1

使用其中之一

• numpy.ravel返回一个连续的展平数组。
• numpy.ndarray.flat返回数组上的一维迭代器。 (这是一个 numpy.flatiter 实例)
• numpy.ndarray.flatten返回折叠成一维数组的副本。

这是一个 MWE。

import numpy as np

lists = [(0, np.array([ [72,  65],
                        [70,  71]], dtype=np.uint8)), 
        (1, np.array([  [71,  99],
                        [190, 163]], dtype=np.uint8))]

l = list()
for idx, array in lists:
    l.append(idx)
    l.extend(np.ravel(array))   # returns a contiguous flattened array
    #l.extend(array.flat)       # return a 1-D iterator over the array.
    #l.extend(array.flatten())  # return a copy of the array collapsed into one dimension 

print(l)
# Output
[0, 72, 65, 70, 71, 1, 71, 99, 190, 163]

---

关于ravel和flatten的区别，摘自What is the difference between flatten and ravel functions in numpy? ,

The difference is that flatten always returns a copy and ravel returns a view of the original array whenever possible. This isn't visible in the printed output, but if you modify the array returned by ravel, it may modify the entries in the original array. If you modify the entries in an array returned from flatten this will never happen. ravel will often be faster since no memory is copied, but you have to be more careful about modifying the array it returns.