python-numpy的基本用法03

python-numpy的基本用法03

线性代数运算

2、随机数产生

3、数组合并拆分

#coding:utf-8
import numpy as np
from arrayIndexAndSlicing import arr

arr1 = np.array([[1, 2, 3], [4, 5, 6]])
arr2 = np.array([[7, 8, 9], [10, 11, 12]])

print np.concatenate([arr1, arr2], axis = 0)  # 按行连接
print np.concatenate([arr1, arr2], axis = 1)  # 按列连接
print np.vstack((arr1, arr2)) # 垂直堆叠=按行连接
print np.hstack((arr1, arr2)) # 水平堆叠=按列连接

print '*' * 50

arr = np.arange(25).reshape(5,5)
print arr
first, second, third = np.split(arr, [1,3], axis = 0) #水平拆分
print first
#[[0 1 2 3 4]]
print second
# [[ 5  6  7  8  9]
#  [10 11 12 13 14]]
print third
# [[15 16 17 18 19]
#  [20 21 22 23 24]]

# 堆叠辅助类
arr = np.arange(6)
arr1 = arr.reshape((3, 2))
arr2 = np.random.randn(3, 2)
print np.r_[arr1, arr2]
# [[ 0.          1.        ]
#  [ 2.          3.        ]
#  [ 4.          5.        ]
#  [ 1.47892319 -0.14980914]
#  [-0.63959067  1.56742361]
#  [ 1.47719175 -0.72199307]]
print 'c_用于按列堆叠'
print np.c_[np.r_[arr1, arr2], arr]
# c_用于按列堆叠
# [[ 0.          1.          0.        ]
#  [ 2.          3.          1.        ]
#  [ 4.          5.          2.        ]
#  [ 1.47892319 -0.14980914  3.        ]
#  [-0.63959067  1.56742361  4.        ]
#  [ 1.47719175 -0.72199307  5.        ]]
print '切片直接转为数组'
print np.c_[1:6, -10:-5]
# 切片直接转为数组
# [[  1 -10]
#  [  2  -9]
#  [  3  -8]
#  [  4  -7]
#  [  5  -6]]

4、repet元素

#coding:utf-8
import numpy as np
import numpy.random as np_random

print 'Repeat: 按元素'
arr = np.arange(3)
print arr.repeat(3)
#[0 0 0 1 1 1 2 2 2]
print arr.repeat([2, 3, 4]) # 3个元素，分别复制2, 3, 4次。长度要匹配！
# [0 0 1 1 1 2 2 2 2]
print

print 'Repeat，指定轴'
arr = np_random.randn(2, 2)
print arr
# [[-1.28463953  0.19053388]
#  [ 1.10101803 -0.18598974]]
print arr.repeat(2, axis = 0) # 按行repeat
# [[-1.28463953  0.19053388]
#  [-1.28463953  0.19053388]
#  [ 1.10101803 -0.18598974]
#  [ 1.10101803 -0.18598974]]
print arr.repeat(2, axis = 1) # 按列repeat
# [[-1.28463953 -1.28463953  0.19053388  0.19053388]
#  [ 1.10101803  1.10101803 -0.18598974 -0.18598974]]
print

print 'Tile: 参考贴瓷砖'
print np.tile(arr, 2)
# [[-1.28463953  0.19053388 -1.28463953  0.19053388]
#  [ 1.10101803 -0.18598974  1.10101803 -0.18598974]]
print np.tile(arr, (2, 3))  # 指定每个轴的tile次数
# [[-1.28463953  0.19053388 -1.28463953  0.19053388 -1.28463953  0.19053388]
#  [ 1.10101803 -0.18598974  1.10101803 -0.18598974  1.10101803 -0.18598974]
#  [-1.28463953  0.19053388 -1.28463953  0.19053388 -1.28463953  0.19053388]
#  [ 1.10101803 -0.18598974  1.10101803 -0.18598974  1.10101803 -0.18598974]]