python - 展平和展平 numpy 数组的嵌套列表

Question

有很多方法可以展平嵌套列表。我在这里复制一个解决方案仅供引用:

def flatten(x):
    result = []
    for el in x:
      if hasattr(el, "__iter__") and not isinstance(el, basestring):
        result.extend(flatten(el))
      else:
        result.append(el)
    return result

我感兴趣的是逆运算，它将列表重建为其原始格式。例如:

L = [[array([[  24, -134],[ -67, -207]])], 
     [array([[ 204,  -45],[  99, -118]])], 
     [array([[  43, -154],[-122,  168]]), array([[  33, -110],[ 147,  -26],[ -49, -122]])]]

# flattened version

L_flat = [24, -134, -67, -207, 204, -45, 99, -118, 43, -154, -122, 168, 33, -110, 147, -26, -49, -122]

是否有一种有效的方法来展平、保存索引并重建其原始格式？

请注意，列表的深度可以是任意的，形状可能不规则，并且将包含不同维度的数组。

当然，flattening 函数也应该更改为存储列表的结构和 numpy 数组的形状。

Answer 1

我一直在寻找一种解决方案来展平和展平 numpy 数组的嵌套列表，但只发现了这个未回答的问题，所以我想到了这个:

def _flatten(values):
    if isinstance(values, np.ndarray):
        yield values.flatten()
    else:
        for value in values:
            yield from _flatten(value)

def flatten(values):
    # flatten nested lists of np.ndarray to np.ndarray
    return np.concatenate(list(_flatten(values)))

def _unflatten(flat_values, prototype, offset):
    if isinstance(prototype, np.ndarray):
        shape = prototype.shape
        new_offset = offset + np.product(shape)
        value = flat_values[offset:new_offset].reshape(shape)
        return value, new_offset
    else:
        result = []
        for value in prototype:
            value, offset = _unflatten(flat_values, value, offset)
            result.append(value)
        return result, offset

def unflatten(flat_values, prototype):
    # unflatten np.ndarray to nested lists with structure of prototype
    result, offset = _unflatten(flat_values, prototype, 0)
    assert(offset == len(flat_values))
    return result

例子:

a = [
    np.random.rand(1),
    [
        np.random.rand(2, 1),
        np.random.rand(1, 2, 1),
    ],
    [[]],
]

b = flatten(a)

# 'c' will have values of 'b' and structure of 'a'
c = unflatten(b, a)

输出:

a:
[array([ 0.26453544]), [array([[ 0.88273824],
       [ 0.63458643]]), array([[[ 0.84252894],
        [ 0.91414218]]])], [[]]]
b:
[ 0.26453544  0.88273824  0.63458643  0.84252894  0.91414218]
c:
[array([ 0.26453544]), [array([[ 0.88273824],
       [ 0.63458643]]), array([[[ 0.84252894],
        [ 0.91414218]]])], [[]]]

许可证:WTFPL