如何获取字符串中所有出现的模式的索引 [英] How to get indexes of all occurrences of a pattern in a string

问题描述

string = "Jack and Jill went up the hill to fetch a pail of water. Jack fell down and broke his crown. And Jill came tumbling after. "
d = string.match(/(jack|jill)/i) # -> MatchData "Jill" 1:"Jill"
d.size # -> 1

这只匹配第一次出现的情况.
string.scan部分地完成了这项工作，但它没有告诉您有关匹配模式索引的任何信息.

This only match the first occurrence it seems.
string.scan does the job partially but it doesn't tell anything about the index of the matched pattern.

如何获取模式的所有匹配实例及其索引(位置)的列表?

How do i get a list of all the matched instances of the pattern and their indices (positions)?

推荐答案

您可以使用.scan和$`全局变量，这表示最后一次成功匹配左侧的字符串，但它在通常的.scan中不起作用，因此您需要此 hack (从此答案):

You can use .scan and $` global variable, which means The string to the left of the last successful match, but it doesn't work inside usual .scan, so you need this hack (stolen from this answer):

string = "Jack and Jill went up the hill to fetch a pail of water. Jack fell down and broke his crown. And Jill came tumbling after. "  
string.to_enum(:scan, /(jack|jill)/i).map do |m,|
  p [$`.size, m]
end

输出:

[0, "Jack"]
[9, "Jill"]
[57, "Jack"]
[97, "Jill"]

UPD:

请注意lookbehind的行为–您获得的是真正匹配的部分的索引，而不是 look 的索引:

Note the behaviour of lookbehind – you get the index of the really matched part, not the look one:

irb> "ab".to_enum(:scan, /ab/     ).map{ |m,| [$`.size, $~.begin(0), m] }
=> [[0, 0, "ab"]]
irb> "ab".to_enum(:scan, /(?<=a)b/).map{ |m,| [$`.size, $~.begin(0), m] }
=> [[1, 1, "b"]]

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