从单词索引获取字符索引

Question

给定文本中单词的索引，我需要获取字符索引。 例如，在下面的文字：

"The cat called other cats." 

“猫”字的指数是1 我需要猫即c的第一个字符的索引，这将是4 我不知道如果这是相关的，但我正在使用python-nltk来获取单词。 现在我能想到这样做的唯一方法是：

- Get the first character, find the number of words in this piece of text 
- Get the first two characters, find the number of words in this piece of text 
- Get the first three characters, find the number of words in this piece of text 
Repeat until we get to the required word. 

但是，这将是非常低效的。 任何想法将不胜感激。

Answer 1

import re 
def char_index(sentence, word_index): 
    sentence = re.split('(\s)',sentence) #Parentheses keep split characters 
    return len(''.join(sentence[:word_index*2])) 

---

>>> s = 'The die has been cast' 
>>> char_index(s,3) #'been' has index 3 in the list of words 
12 
>>> s[12] 
'b' 
>>> 

Answer 2

使用enumerate()

>>> def obt(phrase, indx): 
...  word = phrase.split()[indx] 
...  e = list(enumerate(phrase)) 
...  for i, j in e: 
...    if j == word[0] and ''.join(x for y, x in e[i:i+len(word)]) == word: 
...      return i 
... 
>>> obt("The cat called other cats.", 1) 
4 

Answer 3

您可以使用dict这里：

>>> import re 
>>> r = re.compile(r'\w+') 
>>> text = "The cat called other cats." 
>>> dic = { i :(m.start(0), m.group(0)) for i, m in enumerate(r.finditer(text))} 
>>> dic 
{0: (0, 'The'), 1: (4, 'cat'), 2: (8, 'called'), 3: (15, 'other'), 4: (21, 'cats')} 
def char_index(char, word_ind): 
    start, word = dic[word_ind] 
    ind = word.find(char) 
    if ind != -1: 
     return start + ind 
...  
>>> char_index('c',1) 
4 
>>> char_index('c',2) 
8 
>>> char_index('c',3) 
>>> char_index('c',4) 
21