python 的topk演算法例項
阿新 • • 發佈:2020-04-03
我就廢話不多說了,還是直接看程式碼吧!
#! conding:utf-8 def quick_index(array,start,end): left,right = start,end key = array[left] while left < right: while left < right and array[right] > key: right -= 1 array[left] = array[right] while left < right and array[left] < key: left += 1 array[right] = array[left] array[left] = key return left def min_num(array,m): start,end = 0,len(array) - 1 index = quick_index(array,end) while index != m: if index < m: index = quick_index(array,index+1,end) else: index = quick_index(array,index) print(array[:m]) if __name__ == '__main__': alist = [15,54,26,93,17,77,31,44,55,20] min_num(alist,5)
補充知識:python numpy 求top-k accuracy指標
top-k acc表示在多分類情況下取最高的k類得分的label,與真實值匹配,只要有一個label match,結果就是True。
如對於一個有5類的多分類任務
a_real = 1 a_pred = [0.02,0.23,0.35,0.38,0.02] #top-1 a_pred_label = 3 match = False #top-3 a_pred_label_list = [1,2,3] match = True
對於top-1 accuracy
sklearn.metrics提供accuracy的方法,能夠直接計算得分,但是對於topk-acc就需要自己實現了:
#5類:0,1,2,3,4 import numpy as np a_real = np.array([[1],[2],[1],[3]]) #用隨機數代替分數 random_score = np.random.rand((4,5)) a_pred_score = random_score / random_score.sum(axis=1).reshape(random_score.shape[0],1) k = 3 #top-3 #以下是計算方法 max_k_preds = a_pred_score.argsort(axis=1)[:,-k:][:,::-1] #得到top-k label match_array = np.logical_or.reduce(max_k_preds==a_real,axis=1) #得到匹配結果 topk_acc_score = match_array.sum() / match_array.shape[0]
以上這篇python 的topk演算法例項就是小編分享給大家的全部內容了,希望能給大家一個參考,也希望大家多多支援我們。