教你如何获取numpy array前N个最大值

共计 1648 个字符，预计需要花费 5 分钟才能阅读完成。

主要应用了 argsort() 函数，函数原型：

numpy.argsort(a, axis=-1, kind='quicksort', order=None)
'''
Returns the indices that would sort an array.
Perform an indirect sort along the given axis using the algorithm specified by the kind keyword. It returns an array of indices of the same shape as a that index data along the given axis in sorted order.
'''
Parameters: 
a : array_like
Array to sort.
  
axis : int or None, optional
Axis along which to sort. The default is -1 (the last axis). If None, the flattened array is used.
  
kind : {‘quicksort',‘mergesort',‘heapsort',‘stable'}, optional
Sorting algorithm.
  
order : str or list of str, optional
When a is an array with fields defined, this argument specifies which fields to compare first, second, etc. A single field can be specified as a string, and not all fields need be specified, but unspecified fields will still be used, in the order in which they come up in the dtype, to break ties.
  
Returns: 
index_array : ndarray, int
Array of indices that sort a along the specified axis. If a is one-dimensional, a[index_array] yields a sorted a. More generally, np.take_along_axis(a, index_array, axis=a) always yields the sorted a, irrespective of dimensionality.

import numpy as np
top_k=3
arr = np.array([1, 3, 2, 4, 5])
top_k_idx=arr.argsort()[::-1][0:top_k]
print(top_k_idx)
#[4 3 1]

import numpy as np
a = np.array([1,4,3,5,2])
b = np.argsort(a)
print(b)
print 结果 [0 4 2 1 3]

说明 a[0] 最小，a[3] 最大

import heapq 
a=[43,5,65,4,5,8,87]
re1 = heapq.nlargest(3, a) #求最大的三个元素，并排序
re2 = map(a.index, heapq.nlargest(3, a)) #求最大的三个索引    nsmallest 与 nlargest 相反，求最小
print(re1)
print(list(re2)) #因为 re2 由 map() 生成的不是 list，直接 print 不出来，添加 list() 就行了 

结果：

re1：[87, 65, 43]

re2：[6, 2, 0]

以上为个人经验，希望能给大家一个参考。

阿里云 2 核 2G 服务器 3M 带宽 61 元 1 年，有高配

腾讯云新客低至 82 元 / 年，老客户 99 元 / 年

代金券：在阿里云专用满减优惠券