numpy矩陣的基礎操作

import numpy

#delimiter分隔符，dtype資料格式
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)  #陣列中既等於10又等於5的

print (equal)
equal = (vector==10)|(vector==5)
vector[equal]=1
#將陣列中等於10和5的值換成1
print (vector)
print(matrix)
equal = matrix[:,1]==10
#哪一行的第一列等於10
print (equal)
matrix[equal,1]=1
#將這一行的第一列替換成1
print(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])
#冒號代表所有行
print (matrix[:,1])
print (matrix[:,0:2])

int32

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

#u75代表utf型別

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)   #將字串轉化成浮點型
print (vector.dtype)
print (vector) 
print (vector.sum())
print (vector.mean()) #平均值

12,34,56,78],[11,22,33,44]])

sum = matrix.sum(axis=1)  #指定維度，1代表行，0代表列
print(sum)

[180 110]

word_alcho = numpy.genfromtxt("d:\qiujiahao5.txt",delimiter=" ")

print (word_alcho)#nan代表無法識別的
index = numpy.isnan(word_alcho[:,1])#判斷是否是nan
word_alcho[index,0:2]=0
print (word_alcho)
print (word_alcho.sum())
print (word_alcho.mean())

[[  nan   nan  123.]

[  nan   nan  456.]]
[[   0.    0.  123.]
[   0.    0.  456.]]
579.0
96.5

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