flatten是numpy.ndarray.flatten的一个函数,其官方文档:
ndarray.
flatten
(
order='C'
)
Return a copy of the array collapsed into one dimension.
Parameters: |
order : {‘C’, ‘F’, ‘A’, ‘K’}, optional
‘C’ means to flatten in row-major (C-style) order. ‘F’ means to flatten in column-major (Fortran- style) order. ‘A’ means to flatten in column-major order if a is Fortran contiguous in memory, row-major order otherwise. ‘K’ means to flatten a in the order the elements occur in memory. The default is ‘C’.
|
Returns: |
y : ndarray
A copy of the input array, flattened to one dimension.
|
即该函数返回一个折叠成 一维 的数组。
但是该函数只能适用于numpy对象,即array或者mat,普通的list列表是不行的。
1.用于array:
>>> import numpy as np
>>> alist = [[1,2,3],[5,6,7],[8,9,10]]
>>> ar1 = np.array(alist) #二维数组 m * n 形式
>>> ar1
array([[ 1, 2, 3],
[ 5, 6, 7],
[ 8, 9, 10]])
>>> ar1.flatten()
array([ 1, 2, 3, 5, 6, 7, 8, 9, 10]) #一维数组 1 * n 形式
2.用于矩阵:
>>> ma = np.mat(alist) #二维矩阵 m * n 形式
>>> ma
matrix([[ 1, 2, 3],
[ 5, 6, 7],
[ 8, 9, 10]])
>>> ma1 = ma.flatten() #二维数组,1 * n 形式
>>> ma1
matrix([[ 1, 2, 3, 5, 6, 7, 8, 9, 10]])
>>> ma2 = ma.flatten().A #二维数组
>>> ma2
array([[ 1, 2, 3, 5, 6, 7, 8, 9, 10]])
>>> ma3 = ma.flatten().A[0] #一维数组
>>> ma3
array([ 1, 2, 3, 5, 6, 7, 8, 9, 10])
注:
matrix.A 中的 A :array
表示将矩阵 matrix转换为二维数组
matrix.A[0] :取二维数组中第一行元素
3.用于列表:
>>> alist.flatten() #直接使用,出错
Traceback (most recent call last):
File "
", line 1, in
alist.flatten()
AttributeError: 'list' object has no attribute 'flatten'
使用列表推导式可以达到相同的效果:
>>> [y for x in alist for y in x]
[1, 2, 3, 5, 6, 7, 8, 9, 10]