numpy矩阵的基础操作

import numpy#delimiter分隔符，dtype数据格式word_alcho = numpy.genfromtxt("D:\qiujiahao4.txt",delimiter=",",dtype="str")#print (type(word_alcho))

print (word_alcho[0])

['1' '2' '3' '4' 'qiu']

print (word_alcho[0][1])

2

vector = numpy.array([5,10,15,20])matrix = numpy.array([[5,10,15,20],[1,2,3,4]])print (vector)print (matrix)print (word_alcho)

[ 5 10 15 20][[ 5 10 15 20] [ 1  2  3  4]][['1' '2' '3' '4' 'qiu'] ['1' '2' '3' '4' 'qiu']]

equal = (vector==10)&(vector==5)  #数组中既等于10又等于5的print (equal)equal = (vector==10)|(vector==5)vector[equal]=1  #将数组中等于10和5的值换成1print (vector)print(matrix)equal = matrix[:,1]==10   #哪一行的第一列等于10print (equal)matrix[equal,1]=1   #将这一行的第一列替换成1print(matrix)

[False False False False][ 1  1 15 20][[ 5 10 15 20] [ 1  2  3  4]][ True False][[ 5  1 15 20] [ 1  2  3  4]]

print (matrix.dtype)print (vector[0:3])#冒号代表所有行print (matrix[:,1])print (matrix[:,0:2])

int32[ 1  1 15][1 2][[5 1] [1 2]]

#U75代表utf类型word_alcho = numpy.genfromtxt("D:\qiujiahao5.txt",delimiter=" ",dtype="U75",skip_header=1)

print (word_alcho)

[['qiu' 'man'] ['jia' 'woman']]

vector = numpy.array(["1","2","3"])print (vector.dtype)print (vector)vector = vector.astype(float)   #将字符串转化成浮点型print (vector.dtype)print (vector) print (vector.sum())print (vector.mean()) #平均值

<U1['1' '2' '3']float64[ 1.  2.  3.]6.02.0

matrix = numpy.array([[12,34,56,78],[11,22,33,44]])sum = matrix.sum(axis=1)  #指定维度，1代表行，0代表列print(sum)

[180 110]

word_alcho = numpy.genfromtxt("D:\qiujiahao5.txt",delimiter=" ")print (word_alcho)#nan代表无法识别的index = numpy.isnan(word_alcho[:,1])#判断是否是nanword_alcho[index,0:2]=0print (word_alcho)print (word_alcho.sum())print (word_alcho.mean())

[[  nan   nan  123.] [  nan   nan  456.]][[   0.    0.  123.] [   0.    0.  456.]]579.096.5