计算字符串中列表出现次数的Pythonic方式

Question

从目标字符串的列表中查找字符串出现次数的最佳方法是什么？具体来说，我有一个列表：

string_list = [
    "foo",
    "bar",
    "baz"
]

target_string = "foo bar baz bar"

# Trying to write this function!
count = occurrence_counter(target_string) # should return 4

我想进行优化以最小化速度和内存使用，如果这有所作为的话。就大小而言，我预计string_list最终可能包含数百个子字符串。

Answer 1

这个Python3应该工作：

In [4]: string_list = [
   ...:     "foo",
   ...:     "bar",
   ...:     "baz"
   ...: ]
   ...: 
   ...: set_of_counted_word = set(string_list)
   ...: 
   ...: def occurrence_counter(target_str, words_to_count=set_of_counted_word):
   ...:     return sum(1 for word in target_str.strip().split()
   ...:                if word in words_to_count)
   ...: 
   ...: 
   ...: for target_string in ("foo bar baz bar", " bip foo bap foo dib baz   "):
   ...:     print("Input: %r -> Count: %i" % (target_string, occurrence_counter(target_string)))
   ...: 
   ...: 
Input: 'foo bar baz bar' -> Count: 4
Input: ' bip foo bap foo dib baz   ' -> Count: 3

In [5]:

Answer 2

这是有效的！

def occurrence_counter(target_string):
    return sum(map(lambda x: x in string_list, target_string.split(' ')))

字符串被拆分为标记，然后如果每个标记在列表中，则将其转换为1，否则转换为0。sum函数最后对这些值求和。

编辑：也：

def occurrence_counter(target_string):
    return len(list(filter(lambda x: x in string_list, target_string.split(' '))))

Answer 3

使用拼合的另一种方式。计数器：

from collections import Counter
word_counts = Counter(target_string.split(' '))
total = sum(word_counts.get(w, 0)) for w in string_list)