在神经网络中Python list 常用操作讲解收藏

在神经网络开发中,经常要操作多维列表，常见的有X[:,0]、X[:,1]、X[:,:,0]、X[:,:,1]、X[:,m:n]、X[:,:,m:n]和X[: : -1]
X[:,0];是取二维数组中第一维的所有数据
X[:,1]是取二维数组中第二维的所有数据
X[:,m:n]是取二维数组中第m维到第n-1维的所有数据
X[:,:,0]是取三维矩阵中第一维的所有数据
X[:,:,1]是取三维矩阵中第二维的所有数据
X[:,:,m:n]是取三维矩阵中第m维到第n-1维的所有数据

实例：

#!usr/bin/env python
#encoding:utf-8
from __future__ import division
 
import numpy as np
 
def simple_test():
    '''
    简单的小实验
    '''
    data_list=[[1,2,3],[1,2,1],[3,4,5],[4,5,6],[5,6,7],[6,7,8],[6,7,9],[0,4,7],[4,6,0],[2,9,1],[5,8,7],[9,7,8],[3,7,9]]
    # data_list.toarray()
    data_list=np.array(data_list)
    print 'X[:,0]结果输出为：'
    print data_list[:,0]  
    print 'X[:,1]结果输出为：'
    print data_list[:,1]
    print 'X[:,m:n]结果输出为：'
    print data_list[:,0:1]
    data_list=[[[1,2],[1,0],[3,4],[7,9],[4,0]],[[1,4],[1,5],[3,6],[8,9],[5,0]],[[8,2],[1,8],[3,5],[7,3],[4,6]],
               [[1,1],[1,2],[3,5],[7,6],[7,8]],[[9,2],[1,3],[3,5],[7,67],[4,4]],[[8,2],[1,9],[3,43],[7,3],[43,0]],
               [[1,22],[1,2],[3,42],[7,29],[4,20]],[[1,5],[1,20],[3,24],[17,9],[4,10]],[[11,2],[1,110],[3,14],[7,4],[4,2]]]
    data_list=np.array(data_list)
    print 'X[:,:,0]结果输出为：'
    print data_list[:,:,0] 
    print 'X[:,:,1]结果输出为：'
    print data_list[:,:,1]
    print 'X[:,:,m:n]结果输出为：'
    print data_list[:,:,0:1]
 
 
if __name__ == '__main__':
    simple_test()

输出如下：
X[:,0]结果输出为：

[1 1 3 4 5 6 6 0 4 2 5 9 3]

X[:,1]结果输出为：

[2 2 4 5 6 7 7 4 6 9 8 7 7]

X[:,m:n]结果输出为：

[[1]
 [1]
 [3]
 [4]
 [5]
 [6]
 [6]
 [0]
 [4]
 [2]
 [5]
 [9]
 [3]]

X[:,:,0]结果输出为：

[[ 1  1  3  7  4]
 [ 1  1  3  8  5]
 [ 8  1  3  7  4]
 [ 1  1  3  7  7]
 [ 9  1  3  7  4]
 [ 8  1  3  7 43]
 [ 1  1  3  7  4]
 [ 1  1  3 17  4]
 [11  1  3  7  4]]

X[:,:,1]结果输出为：

[[  2   0   4   9   0]
 [  4   5   6   9   0]
 [  2   8   5   3   6]
 [  1   2   5   6   8]
 [  2   3   5  67   4]
 [  2   9  43   3   0]
 [ 22   2  42  29  20]
 [  5  20  24   9  10]
 [  2 110  14   4   2]]

X[:,:,m:n]结果输出为：

[[[ 1]
  [ 1]
  [ 3]
  [ 7]
  [ 4]]
 
 [[ 1]
  [ 1]
  [ 3]
  [ 8]
  [ 5]]
 
 [[ 8]
  [ 1]
  [ 3]
  [ 7]
  [ 4]]
 
 [[ 1]
  [ 1]
  [ 3]
  [ 7]
  [ 7]]
 
 [[ 9]
  [ 1]
  [ 3]
  [ 7]
  [ 4]]
 
 [[ 8]
  [ 1]
  [ 3]
  [ 7]
  [43]]
 
 [[ 1]
  [ 1]
  [ 3]
  [ 7]
  [ 4]]
 
 [[ 1]
  [ 1]
  [ 3]
  [17]
  [ 4]]
 
 [[11]
  [ 1]
  [ 3]
  [ 7]
  [ 4]]]

X[: : m]代表了[开始：结束：步进]，步进默认为 1

>>>string = 'python'
>>>string[::1]    # 步进为1
 'python'
>>> string[::2]    # 步进为2, [0, 0+2, 0+2+2...]
 'pto'

X[: : -1]将列表或字符反转在操作

>>> list = [1,2,3,4,5,6,7,7,8]
>>> list[::-1][:3]
[8, 7, 7]