Cutting a string at nth occurrence of a character

问题:

What I want to do is take a string such as this.those.that and get a substring to or from the nth occurrence of a character. So, from the start of the string to the 2nd occurrence of . would return this.those. Likewise, from the 2nd occurrence of . to the end of the string would return that. Sorry if my question is foggy, it's not that easy to explain. Also, please do not suggest making extra variables, and the result will be in a string and not an array.

回答1:

You could do it without arrays, but it would take more code and be less readable.

Generally, you only want to use as much code to get the job done, and this also increases readability. If you find this task is becoming a performance issue (benchmark it), then you can decide to start refactoring for performance.

var str = 'this.those.that',
    delimiter = '.',
    start = 1,
    tokens = str.split(delimiter).slice(start),
    result = tokens.join(delimiter); // those.that
    
console.log(result)

// To get the substring BEFORE the nth occurence
var tokens2 = str.split(delimiter).slice(0, start),
    result2 = tokens2.join(delimiter); // this

console.log(result2)

jsFiddle.

回答2:

Try this :

"qwe.fs.xczv.xcv.xcv.x".replace(/([^\.]*\.){3}/, '');
"xcv.xcv.x"

"qwe.fs.xczv.xcv.xcv.x".replace(/([^\.]*\.){**nth**}/, ''); - where is nth is the amount of occurrence to remove.

回答3:

I'm perplexed as to why you want to do things purely with string functions, but I guess you could do something like the following:

//str       - the string
//c         - the character or string to search for
//n         - which occurrence
//fromStart - if true, go from beginning to the occurrence; else go from the occurrence to the end of the string
var cut = function (str, c, n, fromStart) {
    var strCopy = str.slice(); //make a copy of the string
    var index;
    while (n > 1) {
        index = strCopy.indexOf(c)
        strCopy = strCopy.substring(0, index)
        n--;
    }

    if (fromStart) {
        return str.substring(0, index);
    } else {
        return str.substring(index+1, str.length);
    }
}

However, I'd strongly advocate for something like alex's much simpler code.

回答4:

Just in case somebody needs both "this" and "those.that" in a way as alex described in his comment, here is a modified code:

var str = 'this.those.that',
    delimiter = '.',
    start = 1,
    tokens = str.split(delimiter),
      result = [tokens.slice(0, start), tokens.slice(start)].map(function(item) {
    return item.join(delimiter);
  }); // [ 'this', 'those.that' ] 

document.body.innerHTML = result;

回答5:

If you really want to stick to string methods, then:

// Return a substring of s upto but not including
// the nth occurence of c
function getNth(s, c, n) {
  var idx;
  var i = 0;
  var newS = '';
  do {
    idx = s.indexOf(c);
    newS += s.substring(0, idx);
    s = s.substring(idx+1);
  } while (++i < n && (newS += c))
  return newS;
}