CODEWITHSUNDEEP
javascriptarrays
Pradeep
Pradeep

Reputation: 1107

Return all the array indexes of a given element

I wrote the below function which on a given array and value will return array of the indexes of the value in the array. I observed that it is working only for certain elements? 

var arr = [1,2,3,1,2,3,3,4,3]

var findAll = function(arr, val) {
    var results = [];
    var length = arr.length;
    var pos = 0;
    while(pos < length) {
        pos = arr.indexOf(val, pos);
        if (pos == -1) return [];
        results.push(pos);
        pos = pos + 1;
    }
    return results;
}

//Output:

findAll(arr,3)
[2, 5, 6, 8]

findAll(arr,1)
[] // expected [0,3]

findAll(arr,2)
[] // expected [1,4]

findAll(arr,4)
[] // expected [7]

Upvotes: 0

Views: 87

Answers (4)

Larta
Larta

Reputation: 406

This is how to do it. Simply. And doesn't iterate through the whole array.

function check(ar, val){
    var pos = 0;
    var tmp = [];
    pos = ar.indexOf(val, pos);
    while (pos >= 0){
        tmp.push(pos);
        pos = ar.indexOf(val, pos + 1);
    }
return tmp;

(http://jsfiddle.net/daqdm/1)

Upvotes: 0

Gal Ziv
Gal Ziv

Reputation: 7372

the problem you keep on searching till the end of array. if you dont find something you return [].

so if the value you search for is not the last element in array you'll get []

you should change your if to:

if (pos != -1) results.push(pos);

Upvotes: 2

Cerbrus
Cerbrus

Reputation: 72857

Let's give the function a quick rewrite. This is all you need:

var findAll = function(arr, val) {
    var results = [];
    for(var i = 0; i < arr.length; i++){ // Loop through the array.
        if(arr[i] === val){              // If the desired value is found
            results.push(i);             // Push it's index to `results`
        }
    }
    return results;
}

It's probably not the most efficient, since it iterates the entire array no matter what, but it works like a charm.

Upvotes: 1

jcaron
jcaron

Reputation: 17710

The problem is this line:

if (pos == -1) return [];

You should replace it with:

if (pos == -1) break;

or possibly:

if (pos == -1) return results;

Upvotes: 0

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