Loop through array of objects to find object with matching property

Question

I have 1 array, one with a list of all my users with unique IDs. I have an object which contains contains a selected groups information. Part of that information is the owners ID. I'm trying to figure out, how do I get the users's information given the groups owner ID? For example, the student group object has an owner ID of 70, there's a user on my sites who's ID is 70...how do I match them up?

users: 
[  { 
id: 68
name: mike
domain: i:0#.f|admembers|mike.ca
email: mike.ca
isAdmin: False
 }, etc etc ]

selectedGroup:  { 
name: Students
id: 78
description: 
owner: 70
ownerIsUser: True
 }

see deepdash

milahu
– milahu

2022-10-29 09:48:22 +00:00
Commented Oct 29, 2022 at 9:48 — milahu
– milahu, Commented Oct 29, 2022 at 9:48

Elliot Bonneville · Accepted Answer · 2014-01-29 16:45:14Z

29

You'll have to loop through users:

var i = users.length,
    ownerData;

while(i--) {
    if(selectedGroup.owner == users[i].id) {
        ownerData = users[i];
        break;
    }
}

Or you could use Array.filter():

var ownerData = users.filter(function(user) {
    return user.id === selectedGroup.owner;
})[0];

answered Jan 29, 2014 at 16:45

Elliot Bonneville

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5 Comments

Batman Over a year ago

var i = users.length, ownerData; I've never seen anything like this before. What is "i" here?

Elliot Bonneville Over a year ago

It's a quick way of looping through an array--i is initialized to the length of your users array, and it is decremented in the while loop below. When i reaches 0, the loop executes a final time and ends. It loops through the array in reverse.

Batman Over a year ago

I understand the index part, just not the ownerData part. Shouldn't it be declared separately like var i = x.length; var ownerData;

Elliot Bonneville Over a year ago

Oh. I'm using a comma to separate statements, thus removing the need to place them on individual lines (the whitespace is just for readability). It cuts down on the character count, and is a fairly standard way to declare multiple variables.

Batman Over a year ago

Oh I didn't know I could do it like that. Well I knew I could declare multiple empty variables like this var a,b,c,d; but had no clue I could initialize their values too. Cool, thanks for clearing that up.

Barney · Accepted Answer · 2014-01-29 16:53:24Z

In ECMAScript 6, you could use the native Array.find method:

var selectedUser = users.find( function( user ){
  return user.id === 70;
} );

Seeing as only the latest Firefox supports this for the moment, you could use a library like underscore.js:

var selectedUser = _.find( users, function( user ){
  return user.id === 70;
} );

…or you could use a wrapper around the slightly less recent forEach method:

var selectedUser;

users.forEach( function( user ){
  if( user.id === 70 ){
    selectedUser = user;
  }
} );

But if you want to use script that'll support legacy browsers without using libraries, you'll need a for loop:

var selectedUser;

for( var i = 0; i < users.length; i++ ){
  if( users[ i ].id === 70 ){
    selectedUser = users[ i ];

    break;
  }
};

swornabsent · Accepted Answer · 2014-01-29 16:45:35Z

3

Have a look at Underscore.js to trivialize this, like so:

_.findWhere(users, { id: 68 })

Naturally you could pass in a variable to match like:

_.findWhere(users, { id: selectedGroup.owner })

answered Jan 29, 2014 at 16:45

swornabsent

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2 Comments

Elliot Bonneville Over a year ago

Bad form to include a library for one utility function. Maybe take a look at Underscore's implementation of findWhere and copy it out.

swornabsent Over a year ago

I would have suggested having a broader look at the Underscore library as a comment, as it is likely there is more to be gained, but I am not yet able to comment on questions.

Ezequiel · Accepted Answer · 2014-01-29 16:47:37Z

1

You could just loop over the array to match that:

var match = function (array, matchfn) {
    var i;
    for (i in array) {
        if (matchfn(array[i])) {
            return array[i];
        }
    }
};

var user = match(users, function (u) { return u.id == 70; });

answered Jan 29, 2014 at 16:47

Ezequiel

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Comments

Jason P · Accepted Answer · 2014-01-29 16:55:15Z

1

If you have to work with existing javascript objects, I think a brute-force solution is the only option:

var owner;
for(var i = 0; i < users.length; i++) {
    if (users[i].id == selectedGroup.id) {
        owner = users[i];
        break;
    }        
}

if (owner) {
    console.log(owner);
}

Depending on how you use it, it may be more efficient to restructure your first object so you can directly access a property:

var users = {
    "68": {
        id: 68,
        name: 'mike',
        domain: 'i: 0#.f | admembers | mike.ca',
        email: 'mike.ca',
        isAdmin: false
    }
};

var selectedGroup = {
    name: 'Students',
    id: 78,
    description: '',
    owner: 68,
    ownerIsUser: 'True'
};

var owner = users[selectedGroup.owner];

answered Jan 29, 2014 at 16:55

Jason P

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2 Comments

Batman Over a year ago

Holy crap...I really like the idea of restructuring the array into objects. It would probably require I rewrite my services but it might make things simpler later on.

Batman Over a year ago

I'm trying to restructure the object has selected but I'm not sure how to create a new properties from the loop. This is what I tried: jsfiddle.net/pGsc6

Mike T · Accepted Answer · 2016-09-15 15:03:33Z

-1

You can also use Array.prototype.some to compare all of the objects properties to see if they contain equal values.

function haveSameValues(oneObject, anotherObject) {
  var hasDifferentKeyValues = Object.keys(oneObject).some(function(key){ 
    return oneObject[key] !== anotherObject[key]
  });

  return !hasDifferentKeyValues;
}

answered Sep 15, 2016 at 15:03

Mike T

6428 silver badges15 bronze badges

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