python中where函数_Python中numpy.where()函数的使用

Python中的函数数不胜数，今天小编就numpy.where()函数的使用为大家带来讲解。

numpy.where(condition [，x，y])函数返回满足给定条件的输入数组中元素的索引。

参数:condition : When True, yieldx, otherwise yield y.x,y:Values from which to choose. x, y and

condition need to be broadcastable to some shape.

返回:out : [ndarray or tuple of ndarrays] If both x and y are specified, the output array contains elements of x where condition is True, and elements from y elsewhere.

If only condition is given, return the tuple condition.nonzero(), the indices where condition is True.

代码1：

# Python program explaining

# where() function

import numpy as np

np.where([[True, False], [True, True]],

[[1, 2], [3, 4]], [[5, 6], [7, 8]])

输出：

array([[1, 6],

[3, 4]])

代码2：

# Python program explaining

# where() function

import numpy as np

# a is an array of integers.

a = np.array([[1, 2, 3], [4, 5, 6]])

print(a)

print ('Indices of elements <4')

b = np.where(a<4)

print(b)

print("Elements which are <4")

print(a[b])

输出：

[[1 2 3]

[4 5 6]]

Indices of elements <4

(array([0, 0, 0], dtype=int64), array([0, 1, 2], dtype=int64))

Elements which are <4

array([1, 2, 3])

以上就是Python中numpy.where()函数的使用方法。更多Python学习推荐:JQ教程网Python大全。