Get index of parent object in nested object array

Question

I have this array:

[
    { 
        elements: [
            { id: '123', field: 'value' }
            { id: '456', field: 'value' }
        ]
    }
    { 
        elements: [
            { id: '789', field: 'value' }
        ]
    }
]

Now I need to get the index of the first level object searching by an id: searching for id = '456' should give me 0, id = '789' should give me 1

Basically, you want to get the id of the first item in your elements arrays ? — Yassine Badache
– Yassine Badache, Commented Sep 27, 2016 at 9:29
there's no built-in way to do this. You need to loop on the array — laurent
– laurent, Commented Sep 27, 2016 at 9:29
@YassineBadache No, the ID is the value I know. Depending on that id I need to get the index number of its parent object — user3142695
– user3142695, Commented Sep 27, 2016 at 9:31

Nenad Vracar · Accepted Answer · 2016-09-27 09:32:08Z

5

You can do this with findIndex() and some()

var arr = [{
  elements: [{
    id: '123',
    field: 'value'
  }, {
    id: '456',
    field: 'value'
  }]
}, {
  elements: [{
    id: '789',
    field: 'value'
  }]
}]

var i = arr.findIndex(function(o) {
  return o.elements.some(function(e) {
    return e.id == 456;
  })
})

console.log(i)

answered Sep 27, 2016 at 9:32

Nenad Vracar

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1 Comment

doug65536 Over a year ago

findIndex might not exist in all browsers.

Palm · Accepted Answer · 2016-09-27 09:33:48Z

0

Get the feeling that something could be fixed to rethink this. But who knows. 456 should give u id 1 and so should 789 aswell.

var mapped = whatEverObject[0].elements.map(function(obj){ //0 = first 
 return obj.id;
})

console.log(mapped.indexOf(456)) // will give you 1 since id:123 is id 0 in the first elements array.

answered Sep 27, 2016 at 9:33

Palm

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1 Comment

user3142695 Over a year ago

I'm thinking of the first level object. So 456 is in the first object, which should give me a 0

Community · Accepted Answer · 2020-06-20 09:12:55Z

0

You can make a lookup table. It will be much faster if you do several lookups.

Live Example

var table = makeNestedLookupTable(example);
// table[789] would be 1 if the array in the question were "example"

function makeNestedLookupTable(data) {
    return data.reduce(function(lookup, obj, topIndex) {
        return obj.elements.reduce(function(lookup, element) {
            lookup[element.id] = topIndex;
            return lookup;
        }, lookup);
    }, {});
}

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Sep 27, 2016 at 9:36

doug65536

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Comments

ninjawarrior · Accepted Answer · 2016-09-27 09:40:43Z

You can use this function getIndex which loops through the array and matches the id of the element with the given id and returns the index.This solution will work in all browsers.

var arr = [
    { 
        elements: [
            { id: '123', field: 'value' }
            { id: '456', field: 'value' }
        ]
    }
    { 
        elements: [
            { id: '789', field: 'value' }
        ]
    }
];

function getIndex(arr, id) {
    var i, ii, len, elemlen;
    for (i = 0, len = arr.length; i < len; i++) {
        elements = arr[i].elements;
        for (ii = 0, elemlen = elements.length; ii < elemlen; ii++) {
            if (elements[ii].id === id) {
                return i;
            }
        }
    }
}

var index = getIndex(arr, '456');

rushi · Accepted Answer · 2016-09-27 09:42:48Z

0

Here is a generic code where you can send an array and the lookup attribute:

function giveLevel(a,attr){
for(var i=0;i<a.length;i++){
  var o = a[i];
  var tmp = JSON.stringify(o);
  if(tmp.indexOf(attr)!==-1){
    return i;
  }
}
}

var a = [{elements: [
            { id: '123', field: 'value' },
            { id: '456', field: 'value' }
        ]
    },
    { 
        elements: [
            { id: '789', field: 'value' }
        ]
    }
];

giveLevel(a,'"id":"789"'); // returns 1

answered Sep 27, 2016 at 9:42

rushi

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