javascript - Get all occurrences of a substring in a very big string - Stack Overflow

admin管理员组

文章数量:1386760

Something like indexOf, except I need to find all indexes. If there's .indexOf and ,lastIndexOf , shouldn't there be a function to get all index occurences? I couldn't find.

Note that the string is very large, about 1MB in size, so I would need the fastest solution.

To clarify, I need to get all positions of where a substring occurs in a string.

E.g.

var str = "foo bar foo bar"; //the real string is 1MB
var indexes = str.indexOfAll('foo'); //the function I need
console.log(indexes); //should print [0,8];

One thing that es to mind is to use indexOf in a recurring loop, finds the first word, cut the string at the index, then use indexOf again and so on until it finds nothing. I'm not sure about performance (cutting and re-creating large strings).

Something like indexOf, except I need to find all indexes. If there's .indexOf and ,lastIndexOf , shouldn't there be a function to get all index occurences? I couldn't find.

Note that the string is very large, about 1MB in size, so I would need the fastest solution.

To clarify, I need to get all positions of where a substring occurs in a string.

E.g.

var str = "foo bar foo bar"; //the real string is 1MB
var indexes = str.indexOfAll('foo'); //the function I need
console.log(indexes); //should print [0,8];

One thing that es to mind is to use indexOf in a recurring loop, finds the first word, cut the string at the index, then use indexOf again and so on until it finds nothing. I'm not sure about performance (cutting and re-creating large strings).

• javascript

Share Improve this question Follow edited Jun 4, 2019 at 14:52 Maciej Kravchyk asked Jun 4, 2019 at 14:49 Maciej KravchykMaciej Kravchyk 16.8k77 gold badges7171 silver badges8181 bronze badges 11

• indexOf within loop – hindmost Commented Jun 4, 2019 at 14:51
• Yeah I just thought about that edited my answer. But is there something more optimal? – Maciej Kravchyk Commented Jun 4, 2019 at 14:52
• I would disagree about this duplicate. It is about searching for a string in an array, but this question is about searching for a string pattern, which can be achieved using string-search algorithms like Knuth-Morris-Pratt or Boyer-Moore. – Yeldar Kurmangaliyev Commented Jun 4, 2019 at 14:55
• is there something more optimal? IMO loop with indexOf is most optimal. It doesn't cut/re-create strings. Furthermore, it doesn't make redundant iterations if one uses 2nd parameter of indexOf – hindmost Commented Jun 4, 2019 at 14:58
• I'm going to try it and see how much it takes. I didn't know you can use indexOf in a loop just like that. If it takes a lot of time I'm going to try that string search algo. Thanks! – Maciej Kravchyk Commented Jun 4, 2019 at 15:01

 |  Show 6 more ments

2 Answers 2

Sorted by: Reset to default 5

Easy solution:

const str = "...";
const searchKeyword = "...";

const startingIndices = [];

let indexOccurence = str.indexOf(searchKeyword, 0);

while(indexOccurence >= 0) {
    startingIndices.push(indexOccurence);

    indexOccurence = str.indexOf(searchKeyword, indexOccurence + 1);
}

If you need something highly performant, you may look over specific text search/indexing algorithms like Aho–Corasick algorithm or Boyer–Moore string-search algorithm.

Really depends on your use case and if the text you're searching into is changing or is static and can be indexed beforehand for maximum performance.

const IndexString = (str1, str2, output=[]) =>{
  for(let i = 0; i < str1.length -1; i++){
    let arr = [];
    for(let j = i; j < (i+str2.length) & i<str1.length; j++) arr.push(str1[j])
    const findnew = arr.join('');
    if(findnew===str2) output.push(i);
  }
  return output
}

console.log(IndexString("tiktok tok tok tik tok tik", "tik"))

本文标签： javascriptGet all occurrences of a substring in a very big stringStack Overflow