import numpy as np
x = np.arange(16)
x
array([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15])
x[3]
3
x[3:9]
array([3, 4, 5, 6, 7, 8])
x[3:9:2]
array([3, 5, 7])
[x[3],x[5],x[8]]
[3, 5, 8]
ind = [3,5,8]
x[ind]
array([3, 5, 8])
ind = np.array([[0,2],[1,3]])
x[ind]
array([[0, 2],
[1, 3]])
X = x.reshape(4,-1)
X
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11],
[12, 13, 14, 15]])
row = np.array([0,1,2])
col = np.array([1,2,3])
X[row,col]
array([ 1, 6, 11])
X[0,col]
array([1, 2, 3])
X[:2,col]
array([[1, 2, 3],
[5, 6, 7]])
col = [True,False,True,True]
X[1:3,col]
array([[ 4, 6, 7],
[ 8, 10, 11]])
numpy.array的比较
x
array([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15])
x <3
array([ True, True, True, False, False, False, False, False, False,
False, False, False, False, False, False, False])
x > 3
array([False, False, False, False, True, True, True, True, True,
True, True, True, True, True, True, True])
X <=3
array([[ True, True, True, True],
[False, False, False, False],
[False, False, False, False],
[False, False, False, False]])
x>=3
array([False, False, False, True, True, True, True, True, True,
True, True, True, True, True, True, True])
x==3
array([False, False, False, True, False, False, False, False, False,
False, False, False, False, False, False, False])
2 * x == 24 - 4 * x
array([False, False, False, False, True, False, False, False, False,
False, False, False, False, False, False, False])
X
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11],
[12, 13, 14, 15]])
X < 6
array([[ True, True, True, True],
[ True, True, False, False],
[False, False, False, False],
[False, False, False, False]])
x
array([ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15])
np.sum(x <=3)
4
# 只要有一个满足条件，就会返回true
np.any(x==0)
True
np.all(x>=0)
True
X
array([[ 0, 1, 2, 3],
[ 4, 5, 6, 7],
[ 8, 9, 10, 11],
[12, 13, 14, 15]])
np.sum(X %2 ==0)
8
np.sum(X%2 ==0,axis = 0)
array([4, 0, 4, 0])
np.sum(X%2==0,axis = 1)
array([2, 2, 2, 2])
np.sum((x>3)&(x<10))
6
