How to compare objects in JavaScript only for certain properties

Question

I have 2 arrays like below:

a = [
    {id:item, m:1, n:11, o:111},
    {id:item, m:2, n:21, o:211},
    {id:item, m:3, n:31, o:311},
    {id:'group', items:[
        {id:item, m:4, n:41, o:411},
        {id:item, m:5, n:51, o:511}]
    }
];

b = [
    {id:item, m:1, n:11, o:111, p:101},
    {id:item, m:2, n:21, o:211, p:121},
    {id:item, m:3, n:31, o:311, p:131},
    {id:'group', items:[
        {id:item, m:4, n:41, o:411, p:141},
        {id:item, m:5, n:51, o:511, p:151}]
    }
];

I need to compare these arrays for equality with only m,n,o columns. How to do this in optimal way? The output expected here is true, because those fields have the same values.

var a = [
    {id:'item', m:1, n:11, o:111},
    {id:'item', m:2, n:21, o:211},
    {id:'item', m:3, n:31, o:311},
    {id:'group', items:[{id:'item', m:4, n:41, o:411},
    {id:'item', m:5, n:51, o:511},
]}
];

var b = [
    {id:'item', m:1, n:11, o:111, p:101},
    {id:'item', m:2, n:21, o:211, p:121},
    {id:'item', m:3, n:31, o:311, p:131},
    {id:'group', items:[{id:'item', m:4, n:41, o:411, p:141},
    {id:'item', m:5, n:51, o:511, p:151},
]}
];

var output = _.isEqual(a,b);
$('.res').text(output);

<div class='res'>Arrays Equal?</div>

Any help is greatly appreciated.

It's not clear what you want as a result. Do you want to know if all the elements in the two arrays are the same using those columns? Or just want to know which elements are in common? How are the nested objects used, does it have to operate recursively? — Barmar
– Barmar, Commented Jan 30, 2015 at 21:28

Luís Soares · Accepted Answer · 2015-01-30 21:35:28Z

1

you can do it like this (for m comparison):

a[0].m == b[0].m

answered Jan 30, 2015 at 21:35

Luís Soares

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Comments

Rick Hitchcock · Accepted Answer · 2015-01-30 23:10:07Z

You can iterate through the arrays, comparing each object's m, n, and o values.

The difficulty comes with the nested items, which also have m, n, and o properties. In that case, you can call the function recursively on a[i].items and b[i].items.

function equals(a,b) {
  for(var i = 0 ; i < a.length ; i++) {
    if(a[i].items) {
      if(!equals(a[i].items, b[i].items)) {
        return false;
      }
    }
    else if(a[i].m !== b[i].m || a[i].n !== b[i].n || a[i].o !== b[i].o) {
      return false;
    }
  }
  return true;
} //equals

var a = [
    {id:'item', m:1, n:11, o:111},
    {id:'item', m:2, n:21, o:211},
    {id:'item', m:3, n:31, o:311},
    {id:'group', items:[
      {id:'item', m:4, n:41, o:411},
      {id:'item', m:5, n:51, o:511}
    ]}
];

var b = [
    {id:'item', m:1, n:11, o:111, p:101},
    {id:'item', m:2, n:21, o:211, p:121},
    {id:'item', m:3, n:31, o:311, p:131},
    {id:'group', items:[
      {id:'item', m:4, n:41, o:411, p:141},
      {id:'item', m:5, n:51, o:511, p:151}
    ]}
];

alert(equals(a,b));

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