python numpy库中flatten()函数用法

python的numpy库中flatten()函数用法

饕餮争锋

42279人浏览 · 2017-05-16 16:25:33

饕餮争锋 · 2017-05-16 16:25:33 发布

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:

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.

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