Select object by children array and object values

Question

I'm getting data from an object from Facebook, and would like to select all objects in an array, that has a child value of xxx.

The object (simplified of course) is structured like this:

var friends = [
    {
        id: 123456,
        name: "Friend1 name",
        education: [
            {
                school: {
                    name: "School1 name"
                },
                type: "Highscool"
            }
        ]
    },
    {
        id: 3456789,
        name: "Friend2 name",
        education: [
            {
                school: {
                    name: "School2 name"
                },
                type: "College"
            }
        ]
    }
]

Let's assume that I want to get all objects with education.type = "Highscool". How can I do this, without looping though the entire object...?

And how many elements can education have? Should we check only the first one education[0]? — dfsq
– dfsq, Commented Mar 13, 2013 at 9:18
I assume "Highscool" is a typo. :-) I used "Highschool" in my answer, but adjust as necessary. — T.J. Crowder
– T.J. Crowder, Commented Mar 13, 2013 at 9:21

T.J. Crowder · Accepted Answer · 2013-03-13 09:18:54Z

1

How can I do this, without looping though the entire object...?

You can't. But it doesn't have to be hard:

var highSchoolFriends = friends.filter(function(friend) {
    var keep = false;
    friend.education.some(function(entry) {
        if (entry.type === "Highschool") {
            keep = true;
            return true;
        }
    });
    return keep;
});

That uses the ES5 Array#filter and Array#some functions. filter returns a new array made up of the entries in the friends array for which the iterator function returns true. some loops through an array until the iteration function you give it returns true (I used it instead of Array#forEach because you can stop it early). If you need to support older browsers that don't have those yet, they're ones of the ones an "ES5 shim" can give you.

Or you just do the simple loops:

var i, j;
var highSchoolFriends = [];
var friend;

for (i = 0; i < friends.length; ++i) {
    friend = friends[i];
    for (j = 0; j < friend.education.length; ++j) {
        if (friend.education[j].type === "Highschool") {
            highSchoolFriends.push(friend);
            break;
        }
    }
});

edited Mar 13, 2013 at 9:18

answered Mar 13, 2013 at 9:12

T.J. Crowder

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2 Comments

curly_brackets Over a year ago

Thank you for your reply. It's not hard, but my friend list is huge, and the app is for mobiles, so I hoped not to do alot loops. But I guess there is no other way... Thanks for your time.

T.J. Crowder Over a year ago

@KennethB: No worries, hope that helped.

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