# 使用collections.Counter類統計列表元素出現次數
1 from collections import Counter 2 3 4 names = ["Stanley", "Lily", "Bob", "Well", "Peter", "Bob", "Well", "Peter", "Well", "Peter", "Bob", 5 "Stanley", "Lily", "Bob", "Well", "Peter", "Bob", "Bob", "Well", "Peter", "Bob", "Well"] 6 7 names_counts = Counter(names) # 實例化Counter對象，可接收任何hashable序列，Counter對象可以像字典一樣訪問元素並返回出現的次數 8 print(names_counts["Stanley"]) 9 # 2 10 print(names_counts) 11 # Counter({'Bob': 7, 'Well': 6, 'Peter': 5, 'Stanley': 2, 'Lily': 2}) 12 13 top_three = names_counts.most_common(3) # 取出出現次數最多的三個元素 14 print(top_three) 15 # [('Bob', 7), ('Well', 6), ('Peter', 5)] 16 17 more_names = ["Stanley", "Lily", "Bob", "Well"] 18 names_counts.update(more_names) # 使用update方法新增需要統計的序列 19 top_three = names_counts.most_common(3) # 取出出現次數最多的三個元素 20 print(top_three) 21 # [('Bob', 8), ('Well', 7), ('Peter', 5)] 22 23 names_counts = Counter(names) 24 more_names_counts = Counter(more_names) 25 print(names_counts) 26 # Counter({'Bob': 7, 'Well': 6, 'Peter': 5, 'Stanley': 2, 'Lily': 2}) 27 print(more_names_counts) 28 # Counter({'Stanley': 1, 'Lily': 1, 'Bob': 1, 'Well': 1}) 29 print(names_counts - more_names_counts) # 減去次數 30 # Counter({'Bob': 6, 'Well': 5, 'Peter': 5, 'Stanley': 1, 'Lily': 1}) 31 print(names_counts + more_names_counts) # 合並次數 32 # Counter({'Bob': 8, 'Well': 7, 'Peter': 5, 'Stanley': 3, 'Lily': 3})
參考資料：
Python Cookbook, 3rd edition, by David Beazley and Brian K. Jones (O’Reilly).