Merging many arrays into one array (JavaScript)

Question

I'm trying to take an array of many arrays that contain many objects and manipulate it into an array of objects.

So, let's say I have an array that looks like this:

[
    [
        {Name: 'Josh', email: '[email protected]', Points: 33},
        {Name: 'Doug', email: '[email protected]', Points: 12}
    ],
    [
        {Name: 'Josh', email: '[email protected]', Points: 11},
        {Name: 'Doug', email: '[email protected]', Points: 18}
    ],
    [
        {Name: 'Josh', email: '[email protected]', Points: 2},
        {Name: 'Doug', email: '[email protected]', Points: 27}
    ]
]

The Desired outcome would be an array of objects that has a 'Points' property to hold an array of the points. So it would look like this:

[
    {Name: 'Josh', email: '[email protected]', Points: [33, 11, 2]},
    {Name: 'Doug', email: '[email protected]', Points: [12, 18, 27]}
]

This problem seems simple, but I can't seem to figure out the best way of doing this. If you want this data in a fiddle, I made this for you to play with: http://jsfiddle.net/Qhxzz/1/

Do you need recursive flattening, or just one level? Are you using underscore.js or similar? — singpolyma
– singpolyma, Commented Oct 18, 2012 at 16:20
The structure is static. I do not need recursive flattening, and I'm not using any js libraries — frshca
– frshca, Commented Oct 18, 2012 at 16:48

I Hate Lazy · Accepted Answer · 2012-10-18 16:55:38Z

Here's one way using .reduce() and .forEach(). (You'll need patches if you're supporting older browsers.)

var consolidated = data.reduce(function(holder, arr) {
    arr.forEach(function(obj) {
        if (obj.email in holder.emails)
            holder.emails[obj.email].Points.push(obj.Points);
        else {
            holder.emails[obj.email] = obj;
            holder.result.push(obj);
            obj.Points = [obj.Points];
        }
    });
    return holder;
}, {emails:{},result:[]}).result;

And actually, we could flatten out the original Array using concat.apply(), and be left with one monolithic Array to iterate.

flat = [].concat.apply([], data);

This turns your data into this structure:

[{Name:"Josh", email:"[email protected]", Points:33},
 {Name:"Doug", email:"[email protected]", Points:12},
 {Name:"Josh", email:"[email protected]", Points:11},
 {Name:"Doug", email:"[email protected]", Points:18},
 {Name:"Josh", email:"[email protected]", Points:2},
 {Name:"Doug", email:"[email protected]", Points:27}]

And makes the consolidation a bit simpler by eliminating the need for the inner .forEach().

var consolidated = flat.reduce(function(holder, obj) {
    if (obj.email in holder.emails)
        holder.emails[obj.email].Points.push(obj.Points);
    else {
        holder.emails[obj.email] = obj;
        holder.result.push(obj);
        obj.Points = [obj.Points];
    }
    return holder;
}, {emails:{}, result:[]}).result;

jbabey · Accepted Answer · 2012-10-18 16:28:38Z

2

Note that this depends on the input structure being static (no recursion here). Assuming you're not using any libraries:

var result = [];

for (var i = 0; i < initial.length; i++) {
    var innerArray = initial[i];

    for (var j = 0; j < innerArray.length; j++) {
        var item = innerArray[j];

        var found = false;
        // search result for an object with a matching email prop
        for (var k = 0; k < result.length; k++) {
            if (result[k].email === item.email) {
                found = true;

                // add this Point to the Points array
                result[k].Points.push(item.Points);
            }
        }

        if (!found) {
            // convert Points to an array of Points
            item.Points = [item.Points];

            result.push(item);
        }
    }
}

http://jsfiddle.net/Qhxzz/2/

answered Oct 18, 2012 at 16:28

jbabey

46.7k12 gold badges73 silver badges94 bronze badges

1 Comment

Christoph Over a year ago

works fine, would be easier if the result was an object rather than an array.

Collectives™ on Stack Overflow

Merging many arrays into one array (JavaScript)

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related