How can I find out the array position of an object by searching the array?

Question

If I have an array like this:

var array1 = 
[
  {"phraseId":"abc",
  "keyword":"bb",
  "posId":1},
  {"phraseId":"def",
  "keyword":"bb",
  "posId":1},
]

How can I find out that the object with phraseId of "def" has the 2nd position?

Possible duplicate: http://stackoverflow.com/questions/7364150/find-object-by-id-in-an-array-of-javascript-objects — Leroy Thompson, Aug 01 '16 at 18:34

score 6 · Answer 1 · answered Aug 01 '16 at 18:37

6

You could map your object and only return the target field, and then use the built in indexOf to get the position:

array1.map(item => item.phraseId).indexOf('def')

answered Aug 01 '16 at 18:37

Rob M.

35,491
6
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1

Not downvoting, but this results in 2 iterations of the array as well as the allocation of more memory for the 2nd mapped array, which is unnecessary. – Ryan Wheale Aug 01 '16 at 18:53

Pranav C Balan · Accepted Answer · 2016-08-01T18:55:17.887

5

Use native JavaScript findIndex method.

var array1 = [{
  "phraseId": "abc",
  "keyword": "bb",
  "posId": 1
}, {
  "phraseId": "def",
  "keyword": "bb",
  "posId": 1
}, ];

var pos = array1.findIndex(function(v) {
  // set your condition for finding object             
  return v.phraseId == 'def';
  // add `1` since you want to count from `1`            
}) + 1;

console.log("Position of the object " + pos);

For older browser check polyfill option.

With ES6 arrow function

var array1 = [{
  "phraseId": "abc",
  "keyword": "bb",
  "posId": 1
}, {
  "phraseId": "def",
  "keyword": "bb",
  "posId": 1
}, ];

var pos = array1.findIndex(v => v.phraseId == 'def') + 1;

console.log("Position of the object " + pos);

edited Aug 01 '16 at 18:55

answered Aug 01 '16 at 18:37

Pranav C Balan

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2

I did not know that `findIndex` was an official ECMAScript 6 thing. Neat. – StriplingWarrior Aug 01 '16 at 18:40
1

I think this solution better than `.map()` because `findIndex()` it's native JS method returns an index in the array unlike `.map` wich used for array iteration. Interesting to see some benchmarks of this two methods. – semanser Aug 01 '16 at 18:44
Since we're using the latest cool stuff, why not write it the easy way: `var pos = array1.findIndex(v => v.phraseId === 'def');` – Ryan Wheale Aug 01 '16 at 18:51

score 1 · Answer 3 · answered Aug 01 '16 at 18:38

1

It works this way :

array1.forEach((elem, index) => {if (elem.phraseId === "def")
   console.log("index = " + index);
});

answered Aug 01 '16 at 18:38

kevin ternet

4,514
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score 1 · Answer 4 · answered Aug 01 '16 at 18:40

Assuming that your key is know (that you know you are looking for a phraseId always) then you can simply iterate through the array with a normal for loop if you are using "traditional" JS, or with a forEach if you are using ES6. Here's the simple for implementation.

for (var i = 0; i < array1.length; i++ ){
    if(array[i].phraseId === 'def') {
    // we know "i" is the index, so do something...
    }
}

To make it more generic so you can search any array for any key, make a function of it that returns the index:

function whatIndex (arr, key, val) {
    for (var i = 0; i < arr.length; i++) {
        if( arr[i][key] === val ) {
            return i;
        }
    }
}

How can I find out the array position of an object by searching the array?

4 Answers4