arrays - 为什么不使用 .map 从 stringArray 中删除最后一个句号

Question

我正在使用 Swift。 我正在尝试将一个句子转换为一个字符串数组。我使用 map 将句点和逗号与单词分开，如下所示:

extension String  {


func convertSentenceToArray()-> [String] {
var sentence = String(self)

sentence.index(of: ".").map { 
   sentence.remove( at: $0)
   sentence.insert(".", at: $0)
   sentence.insert(" ", at: $0)
   }
sentence.index(of: ",").map { 
  sentence.remove( at: $0)
  sentence.insert(",", at: $0)
  sentence.insert(" ", at: $0) 
   }
 return sentence.components(separatedBy: " ")
 }
}

let  thisSentenceString = "I am trying to create an array from a sentence. But I don't understand, Why isn't the last fullstop removed, from the last word."

let thisSentenceArray = thisSentenceString.convertSentenceToArray()

print(thisSentenceArray)

结果:

["I", "am", "trying", "to", "create", "an", "array", "from", "a", "sentence", ".", "But", "I", "don\'t", "understand", ",", "Why", "isn\'t", "the", "last", "fullstop", "removed,", "from", "the", "last", "word."]

除最后一个外，所有句点和逗号都按我预期的方式处理。

我不明白为什么最后一个句号仍然存在。虽然我可以找到解决此问题的方法，但我想了解我所采用的方法有什么问题。

Answer 1

首先解释一下你的代码做了什么:

sentence
   .index(of: ".") // find the first index of the dot character
   .map {  // Optional.map, if the index exists, do the following
      sentence.remove( at: $0) // remove dot
      sentence.insert(".", at: $0) // insert dot again
      sentence.insert(" ", at: $0) // insert space
   }

或重写:

if let firstDotIndex = sentence.index(of: ".") {
    sentence.insert(" ", at: firstDotIndex)
}

这意味着只找到并替换第一个点字符。

要正确执行此算法，您需要:

// helper method checking punctuation to avoid code duplication
let isPunctuation: (Character) -> Bool = {
    return [".", ","].contains($0)
}

// initial range, we want to check the entire string
var range = sentence.startIndex...

// iterate while some punctuation exists
while let punctuationIndex = sentence[range].index(where: isPunctuation) {
    // insert the separator
    sentence.insert(" ", at: punctuationIndex)
    // search next punctuation only from the last replacement
    range = sentence.index(after: punctuationIndex)...
}

不过，其实已经有String替换的方法了:

sentence = sentence.replacingOccurrences(of: ".", with: " .")

或者更简单，用一个正则表达式一次性覆盖所有标点符号:

return self
    .replacingOccurrences(of: "[,.]", with: " $0", options: .regularExpression)
    .components(separatedBy: " ")