NumPy numpy.unique 函数

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  简述

  此函数返回输入数组中唯一元素的数组。该函数能够返回唯一值数组的元组和关联索引的数组。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)
  

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  函数说明

  序号	参数及说明
  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，则返回唯一数组的索引，可用于重构输入数组
  4	return_counts 如果为 True，则返回唯一数组中的元素在原始数组中出现的次数

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  例子

  
  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
  

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  它的输出如下 -

  
  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]
  

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