python numpy数组求和_【numpy求和】numpy.sum()求和

#example

import numpy as np

x = np.random.rand(2,3,4) #生成三维随array

print("This is a 2*3rows 4cols array\n",x)

'''

>>> This is a 2*3rows 4cols array

[[[ 0.88264952 0.12446208 0.82166137 0.31747846]

[ 0.51436626 0.03051283 0.46987831 0.64086531]

[ 0.14819094 0.6395191 0.21753309 0.61340538]]

[[ 0.0878878 0.5317064 0.65523138 0.704961 ]

[ 0.51081521 0.88710145 0.92958269 0.89587262]

[ 0.60233393 0.26146419 0.26584161 0.0823285 ]]]

'''

print('instance method:',x.sum())

print('numpy function:',np.sum(x))

'''

>>> 'instance method:', 11.835649415181807

>>> 'numpy function:', 11.835649415181807

'''

#对特定的轴求和

print('First axis sum',x.sum(axis=0))

'''

>>> 'First axis sum', #第一维是轴0，对前后两页array加和得到3*4的array输出

array([[ 0.97053732, 0.65616848, 1.47689275, 1.02243946],

[ 1.02518147, 0.91761428, 1.399461 , 1.53673793],

[ 0.75052486, 0.90098329, 0.4833747 , 0.69573388]])

'''

print('Second axis sum',x.sum(axis=1))

'''

>>> 'Second axis sum', #第二维是轴1，将每列的三行进行sum(对行求sum)，得到2*4的输出

array([[ 1.54520672, 0.79449401, 1.50907277, 1.57174914],

[ 1.20103694, 1.68027204, 1.85065568, 1.68316212]])

'''

print('Third axis sum',x.sum(axis=2))

'''

>>> 'Third axis sum', #第三维是轴2，有4个数，将每行四个数加和(对列求sum)，得到2*3输出

array([[ 2.14625142, 1.65562271, 1.6186485 ],

[ 1.97978658, 3.22337197, 1.21196823]])

'''

#对多个轴求和

print('axis1,2 sum:',x.sum(axis=(1,2)))

'''

>>> 'axis1,2 sum: #对第二维(axis=1)和第三维(axis=2)求和，归在第一维(axis=0)上

array([ 5.42052263, 6.41512678])

'''