NumPy 数组操作 numpy.unique

该函数返回输入数组中唯一元素的数组。该函数能够返回一个包含唯一值数组和关联索引数组的元组。索引的性质取决于函数调用中返回参数的类型。

numpy.unique(arr, return_index, return_inverse, return_counts)

其中，

序号	参数和描述
1	arr 输入数组。如果不是一维数组，将被展平
2	return_index 如果为True，则返回输入数组中元素的索引
3	return_inverse 如果为True，则返回数组中唯一元素的索引，可以用来重构输入数组
4	return_counts 如果为True，则返回原始数组中唯一数组元素出现的次数

示例

import numpy as np 
a = np.array([5,2,6,2,7,5,6,8,2,9]) 

print 'First array:' 
print a 
print '\n'  

print 'Unique values of first array:' 
u = np.unique(a) 
print u 
print '\n'  

print 'Unique array and Indices array:' 
u,indices = np.unique(a, return_index = True) 
print indices 
print '\n'  

print 'We can see each number corresponds to index in original array:' 
print a 
print '\n'  

print 'Indices of unique array:' 
u,indices = np.unique(a,return_inverse = True) 
print u 
print '\n' 

print 'Indices are:' 
print indices 
print '\n'  

print 'Reconstruct the original array using indices:' 
print u[indices] 
print '\n'  

print 'Return the count of repetitions of unique elements:' 
u,indices = np.unique(a,return_counts = True) 
print u 
print indices

它的输出如下所示−

First array:
[5 2 6 2 7 5 6 8 2 9]

Unique values of first array:
[2 5 6 7 8 9]

Unique array and Indices array:
[1 0 2 4 7 9]

We can see each number corresponds to index in original array:
[5 2 6 2 7 5 6 8 2 9]

Indices of unique array:
[2 5 6 7 8 9]

Indices are:
[1 0 2 0 3 1 2 4 0 5]

Reconstruct the original array using indices:
[5 2 6 2 7 5 6 8 2 9]

Return the count of repetitions of unique elements:
[2 5 6 7 8 9]
 [3 2 2 1 1 1]