问题
I\'m trying to find the positions of all occurrences of a string in another string, case-insensitive.
For example, given the string:
I learned to play the Ukulele in Lebanon.
and the search string le, I want to obtain the array:
[2, 25, 27, 33]
Both strings will be variables - i.e., I can\'t hard-code their values.
I figured that this was an easy task for regular expressions, but after struggling for a while to find one that would work, I\'ve had no luck.
I found this example of how to accomplish this using .indexOf(), but surely there has to be a more concise way to do it?
回答1:
var str = "I learned to play the Ukulele in Lebanon."
var regex = /le/gi, result, indices = [];
while ( (result = regex.exec(str)) ) {
indices.push(result.index);
}
UPDATE
I failed to spot in the original question that the search string needs to be a variable. I've written another version to deal with this case that uses indexOf, so you're back to where you started. As pointed out by Wrikken in the comments, to do this for the general case with regular expressions you would need to escape special regex characters, at which point I think the regex solution becomes more of a headache than it's worth.
function getIndicesOf(searchStr, str, caseSensitive) {
var searchStrLen = searchStr.length;
if (searchStrLen == 0) {
return [];
}
var startIndex = 0, index, indices = [];
if (!caseSensitive) {
str = str.toLowerCase();
searchStr = searchStr.toLowerCase();
}
while ((index = str.indexOf(searchStr, startIndex)) > -1) {
indices.push(index);
startIndex = index + searchStrLen;
}
return indices;
}
var indices = getIndicesOf("le", "I learned to play the Ukulele in Lebanon.");
document.getElementById("output").innerHTML = indices + "";<div id="output"></div>回答2:
Here is regex free version:
function indexes(source, find) {
if (!source) {
return [];
}
// if find is empty string return all indexes.
if (!find) {
// or shorter arrow function:
// return source.split('').map((_,i) => i);
return source.split('').map(function(_, i) { return i; });
}
var result = [];
for (i = 0; i < source.length; ++i) {
// If you want to search case insensitive use
// if (source.substring(i, i + find.length).toLowerCase() == find) {
if (source.substring(i, i + find.length) == find) {
result.push(i);
}
}
return result;
}
indexes("I learned to play the Ukulele in Lebanon.", "le")
EDIT: and if you want to match strings like 'aaaa' and 'aa' to find [0, 2] use this version:
function indexes(source, find) {
if (!source) {
return [];
}
if (!find) {
return source.split('').map(function(_, i) { return i; });
}
var result = [];
var i = 0;
while(i < source.length) {
if (source.substring(i, i + find.length) == find) {
result.push(i);
i += find.length;
} else {
i++;
}
}
return result;
}
回答3:
You sure can do this!
//make a regular expression out of your needle
var needle = 'le'
var re = new RegExp(needle,'gi');
var haystack = 'I learned to play the Ukulele';
var results = new Array();//this is the results you want
while (re.exec(haystack)){
results.push(re.lastIndex);
}
Edit: learn to spell RegExp
Also, I realized this isn't exactly what you want, as lastIndex tells us the end of the needle not the beginning, but it's close - you could push re.lastIndex-needle.length into the results array...
Edit: adding link
@Tim Down's answer uses the results object from RegExp.exec(), and all my Javascript resources gloss over its use (apart from giving you the matched string). So when he uses result.index, that's some sort of unnamed Match Object. In the MDC description of exec, they actually describe this object in decent detail.
回答4:
If you just want to find the position of all matches I'd like to point you to a little hack:
haystack = 'I learned to play the Ukulele in Lebanon.'
needle = 'le'
splitOnFound = haystack.split(needle).map(function (culm) {
return this.pos += culm.length + needle.length
}, {pos: -needle.length}).slice(0, -1)
it might not be applikable if you have a RegExp with variable length but for some it might be helpful.
回答5:
Use String.prototype.match.
Here is an example from the MDN docs itself:
var str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
var regexp = /[A-E]/gi;
var matches_array = str.match(regexp);
console.log(matches_array);
// ['A', 'B', 'C', 'D', 'E', 'a', 'b', 'c', 'd', 'e']
回答6:
Follow the answer of @jcubic, his solution caused a small confuse for my case
For example var result = indexes('aaaa', 'aa') it will return [0, 1, 2] instead of [0, 2]
So I updated a bit his solution as below to match my case
function indexes(text, subText, caseSensitive) {
var _source = text;
var _find = subText;
if (caseSensitive != true) {
_source = _source.toLowerCase();
_find = _find.toLowerCase();
}
var result = [];
for (var i = 0; i < _source.length;) {
if (_source.substring(i, i + _find.length) == _find) {
result.push(i);
i += _find.length; // found a subText, skip to next position
} else {
i += 1;
}
}
return result;
}
回答7:
Here is a simple Code
function getIndexOfSubStr(str, serchToken, preIndex, output){
var result = str.match(serchToken);
if(result){
output.push(result.index +preIndex);
str=str.substring(result.index+serchToken.length);
getIndexOfSubStr(str, serchToken, preIndex, output)
}
return output;
};
var str = "my name is 'xyz' and my school name is 'xyz' and my area name is 'xyz' ";
var serchToken ="my";
var preIndex = 0;
console.log(getIndexOfSubStr(str, serchToken, preIndex, []));回答8:
Thanks for all the replies. I went through all of them and came up with a function that gives the first an last index of each occurrence of the 'needle' substring . I am posting it here in case it will help someone.
Please note, it is not the same as the original request for only the beginning of each occurrence. It suits my usecase better because you don't need to keep the needle length.
function findRegexIndices(text, needle, caseSensitive){
var needleLen = needle.length,
reg = new RegExp(needle, caseSensitive ? 'gi' : 'g'),
indices = [],
result;
while ( (result = reg.exec(text)) ) {
indices.push([result.index, result.index + needleLen]);
}
return indices
}
回答9:
One liner using String.protype.matchAll (ES2020):
[...sourceStr.matchAll(new RegExp(searchStr, 'gi'))].map(a => a.index)
Using your values:
const sourceStr = 'I learned to play the Ukulele in Lebanon.';
const searchStr = 'le';
const indexes = [...sourceStr.matchAll(new RegExp(searchStr, 'gi'))].map(a => a.index);
console.log(indexes); // [2, 25, 27, 33]
If you're worried about doing a spread and a map() in one line, I ran it with a for...of loop for a million iterations (using your strings). The one liner averages 1420ms while the for...of averages 1150ms on my machine. That's not an insignificant difference, but the one liner will work fine if you're only doing a handful of matches.
See matchAll on caniuse
回答10:
the below code will do the job for you :
function indexes(source, find) {
var result = [];
for(i=0;i<str.length; ++i) {
// If you want to search case insensitive use
// if (source.substring(i, i + find.length).toLowerCase() == find) {
if (source.substring(i, i + find.length) == find) {
result.push(i);
}
}
return result;
}
indexes("hello, how are you", "ar")
回答11:
function countInString(searchFor,searchIn){
var results=0;
var a=searchIn.indexOf(searchFor)
while(a!=-1){
searchIn=searchIn.slice(a*1+searchFor.length);
results++;
a=searchIn.indexOf(searchFor);
}
return results;
}
来源：https://stackoverflow.com/questions/3410464/how-to-find-indices-of-all-occurrences-of-one-string-in-another-in-javascript