How to get the position of the second occurrence?

Question

Let's say I have this array:

var a = [1,2,99,3,4,99,5];

I would like to get the position of the second 99, something like:

a.indexOf(99, 2) // --> 5

However the second argument in indexOf just tells where to start the search. Is there any built in functions to make this? If not how would you do it?

Thanks!

`a.indexOf(99, a.indexOf(99)+1)` – John Dvorak Jan 23 '13 at 12:26 — John Dvorak, Jan 23 '13 at 12:26

score 6 · Accepted Answer · answered Jan 23 '13 at 12:26

6

There's only indexOf and lastIndexOf. You could loop over it:

var a = [1,2,99,3,4,99,5];
var matches = []
for (var i=0; i<a.length; i++){
    if (a[i] == 99) {
        matches.push(i)
    }
}
console.log(matches); // [2, 5]

If you always want the second occurrence Jan's method is also good:

a.indexOf(99, a.indexOf(99) + 1)

The indexOf call on the right finds the first occurrence, +1 then limits the search to the elements that follow it.

answered Jan 23 '13 at 12:26

Matt Zeunert

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actually your answer is right, however I just realized that I'm looking for something else http://stackoverflow.com/questions/14480345/regex-how-to-get-the-nth-occurrence-in-a-string – Adam Halasz Jan 23 '13 at 13:01
@Adam: You could use my answer together with `strpos` insead of `indexOf`: http://php.net/manual/en/function.strpos.php – Felix Kling Jan 23 '13 at 13:09
@Adam: Oops... then just keep using `indexOf` ;) Sorry, got confused for a second. My solution works for strings as well (as long as you don't want to consider word boundaries). Just sayin' :) – Felix Kling Jan 23 '13 at 13:10

score 2 · Answer 2 · edited May 23 '17 at 12:12

There is no built in function, but you can easily create your own, by iteratively applying indexOf:

function indexOfOccurrence(haystack, needle, occurrence) {
    var counter = 0;
    var index = -1;
    do {
        index = haystack.indexOf(needle, index + 1);
    }
    while (index !== -1 && (++counter < occurrence));
    return index;
}

// Usage
var index = indexOfOccurrence(a, 99, 2);

But Matt's solution might be more useful.

How to get the position of the second occurrence?

2 Answers2