Remove objects from array of object in javascript

Question

I'm trying to remove objects from an array of object using a delta data i'm getting from server. I'm using underscore in my project.

Is there a straight forward way to do this, rather going with looping and assigning ?

Main Array

var input = [
   {name: "AAA", id: 845,status:1},
   {name: "BBB", id: 839,status:1},
   {name: "CCC", id: 854,status:1}
];

Tobe Removed

var deltadata = [
   {name: "AAA", id: 845,status:0},
   {name: "BBB", id: 839,status:0}
];

Expected output

var finaldata =  [
  {name: "CCC", id: 854,status:1}
]

Use Array.prototype.filter with a predicate that performs a .indexOf on the other array. — Benjamin Gruenbaum
– Benjamin Gruenbaum, Commented Apr 16, 2014 at 20:36
What's a delta data? @BenjaminGruenbaum - Could you show an example with indexOf and objects ? — adeneo
– adeneo, Commented Apr 16, 2014 at 20:38
@adeneo Delta is a common term for 'difference' or subtraction - in this case, element subtraction. OP wants to remove all elements from input that do not appear in deltadata - either based on structural equality (in which case you'd .map(JSON.stringify) before performing a .indexOf and stringify the value too, or reference equality - in which case you'd use a simple .indexOf — Benjamin Gruenbaum
– Benjamin Gruenbaum, Commented Apr 16, 2014 at 20:42
@BenjaminGruenbaum - I'm really not getting it, how would you use indexOf for that? Could you post an example, I'm really asking because I'm curious as to how something like that would work? I would think you'd have to compare the ID's or something, as two objects can't be compared with indexOf, and even if you stringify them there's no guarantee they will be equal, even if they contain the exact same things ? — adeneo
– adeneo, Commented Apr 16, 2014 at 20:47
@BenjaminGruenbaum—a simple indexOf won't work because comparing objects will always be false, and JSON.stringify won't be reliable because objects with the same name/value pairs may be returned in a different order. The OP will need to loop over each property in each object to test equality (unless equality depends on just one name/value pair). — RobG
– RobG, Commented Apr 16, 2014 at 20:49

Thad Blankenship · Accepted Answer · 2014-04-16 21:02:24Z

2

Try this

var finaldata = _.filter(input, function(item) {
    return !(_.findWhere(deltadata, {id: item.id}));
});

It does assume that you have unique ID's. Maybe you can come up with something better.

answered Apr 16, 2014 at 21:02

Thad Blankenship

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Comments

silverwind · Accepted Answer · 2014-04-16 21:16:07Z

1

Here's a simple solution. As others have mentioned, I don't think this is possible without a loop. You could also add checks for status and name in the condition, as this just compares IDs.

var finaldata = input.filter(function(o) {
    for (var i = 0; i < deltadata.length; i++)
       if (deltadata[i].id === o.id) return false;
    return true;
});

answered Apr 16, 2014 at 21:16

silverwind

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Bergi · Accepted Answer · 2014-04-16 20:57:12Z

1

A simple filter will do it:

var finaldata = _.filter(input, function(o) {
    return _.findWhere(deltadata, o) === undefined;
});

A little more efficient than the findWhere would be creating a lookup map with ids to remove, and then filtering by that:

var idsToRemove = _.reduce(deltadata, function(m, o) {
    m[o.id] = true;
    return m;
}, {});
var finaldata = _.reject(input, function(o) { return o.id in idsToRemove; });

answered Apr 16, 2014 at 20:57

Bergi

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2 Comments

tomalex Over a year ago

if you compare both input and delta data status field value is going to differ. Your second update looks promising, let me test it out :)

Bergi Over a year ago

uh, I had expected a delta to be "the things that are removed". You still could do a _.findWhere(deltadata, _.pick(o, "name", "id")) or something.

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