NumPy 索引，切片和迭代-蒲公英云

NumPy 索引，切片和迭代

末蓝、 2022-07-11 04:26 281阅读 0赞

索引，切片和迭代

一维数组可以被索引、切片和迭代，就像列表和其它Python序列。

>>> a = arange(10)**3 >>> a array([ 0, 1, 8, 27, 64, 125, 216, 343, 512, 729]) >>> a[2] 8 >>> a[2:5] array([ 8, 27, 64]) >>> a[:6:2] = -1000 # equivalent to a[0:6:2] = -1000; from start to position 6, exclusive, set every 2nd element to -1000 >>> a array([-1000, 1, -1000, 27, -1000, 125, 216, 343, 512, 729]) >>> a[ : :-1] # reversed a array([ 729, 512, 343, 216, 125, -1000, 27, -1000, 1, -1000]) >>> for i in a: ... print i**(1/3.), ... nan 1.0 nan 3.0 nan 5.0 6.0 7.0 8.0 9.0

a = random.random((2,3))
a
array([[ 0.36639821, 0.44035901, 0.74424943],
[ 0.74506957, 0.9945401 , 0.59842882]])
a.sum()
3.8890451481386368
a.min()
0.36639821076181855
a.max()
0.99454010014688865
b = arange(12).reshape(3,4)
b
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11]])
b.sum()
66
b.sum(0)
array([12, 15, 18, 21])
b.sum(1)
array([ 6, 22, 38])
b.min(0)
array([0, 1, 2, 3])
b.min(1)
array([0, 4, 8])
B=array([1,4,9])
sqrt(B)
array([ 1., 2., 3.])
C=array([9,1,4])
c
array([ 1. , 2.57079633, 4.14159265])
C
array([9, 1, 4])
add(B,C)
array([10, 5, 13])
C
array([9, 1, 4])
B
array([1, 4, 9])
C=array([9,4,1])
add(B,C)
array([10, 8, 10])
a = arange(10)
a
array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])
b=a**2
b
array([ 0, 1, 4, 9, 16, 25, 36, 49, 64, 81])
c=b**3
c
array([ 0, 1, 64, 729, 4096, 15625, 46656, 117649,
262144, 531441])
c=a**3
c
array([ 0, 1, 8, 27, 64, 125, 216, 343, 512, 729])
c[2]
8
c[0]
0
c[7]
343
c[2:3]
array([8])
c[0:3]
array([0, 1, 8])
c
array([ 0, 1, 8, 27, 64, 125, 216, 343, 512, 729])
c[2]=-1000
c
array([-1000, 1, -1000, 27, -1000, 125, 216, 343, 512, 729])
c[::-1]
array([ 729, 512, 343, 216, 125, -1000, 27, -1000, 1, -1000])
c
array([-1000, 1, -1000, 27, -1000, 125, 216, 343, 512, 729])
c
array([-1000, 1, -1000, 27, -1000, 125, 216, 343, 512, 729])