Create array where keys match

Question

I have two arrays of objects:

var arOne = [
    {key: 'alpha', value: 5},  
    {key: 'beta', value: 11},  
    {key: 'gamma', value: 15},  
    {key: 'delta', value: 12},  
    {key: 'epsilon', value: 55}  
    {key: 'pony', value: 101}
]

var arTwo = [
    {key: 'alpha', value: 5.5},  
    {key: 'beta', value: 11.5},  
    {key: 'gamma', value: 15.5},  
    {key: 'psi', value: 12.5},  
    {key: 'omega', value: 55.5}  
]

I need to merge values into one array of arrays.

Case where the keys match: create an array with the key and append the value from arTwo to arOne.

Case where the keys do not match: if the key exists in arOne, I include the value from arOne and a 0 for arTwo. If the key exists in arTwo, I include a 0 for arOne and the value from arTwo.

Note that arOne and arTwo may be different sizes (see the pony key in arOne).

This is what the result should look like:

var result = [
    ['alpha', 5, 5.5],  
    ['beta', 11, 11.5],  
    ['gamma', 15, 15.5],  
    ['delta', 12, 0],  
    ['epsilon', 55, 0],  
    ['pony', 101, 0],
    ['psi', 0, 12.5],  
    ['omega', 0, 55.5],  
]

I've been staring at this all day and scratched all my attempts. Any thoughts?

What have you tried? I would suggest two loops, one looping through the first array and populating result, and the other looping through the second and adding new entries to result. — Blazemonger
– Blazemonger, Commented Dec 7, 2012 at 19:38
I tried $.each() which didn't work because the arrays are different sizes. I tried a nested for loop but couldn't figure out how to access the values in the objects. I was hoping jQuery had a semi-elegant solution but perhaps not. — Jason Strimpel
– Jason Strimpel, Commented Dec 7, 2012 at 19:48

FixMaker · Accepted Answer · 2012-12-08 22:04:55Z

2

function combine(obj1, obj2){
    var arr = [], k, i;
    for (k = 0; k < obj1.length; ++k){
        arr.push([obj1[k].key, obj1[k].value]);
    }
    for (k = 0; k < obj2.length; ++k){
        var exists = false;
        for (i = 0; i < arr.length; ++i){
            if(arr[i][0] === obj2[k].key){
               arr[i].push(obj2[k].value);
               var exists = true; 
               break;
            }
        }
        if (!exists){
            arr.push([obj2[k].key, 0, obj2[k].value]);
        }
    }
    for (i = 0; i < arr.length; ++i){
        if (arr[i].length === 2){
            arr[i].push(0);
        }
    }

    return arr;
}

Call like:

var myNewArray = combine(arOne, arTwo);

edited Dec 8, 2012 at 22:04

FixMaker

3,9284 gold badges32 silver badges48 bronze badges

answered Dec 7, 2012 at 19:59

Randy Hall

8,33723 gold badges88 silver badges175 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Randy Hall Over a year ago

This doesn't work. It's doesn't give the 0 for the missing value the OP wanted. Shame on me. I shall edit.

Mathias Over a year ago

I could be mistaking, but the way I see it your first loop pushes the index k into the array instead of the value obj1[k].key.

Mathias Over a year ago

You have to consider that he is asking to merge to arrays full of objects.

Randy Hall Over a year ago

@Mathias fixed! yeah, I missed that array of objects thing, thought it was straight objects at first.

Mathias Over a year ago

I know - I did the same thing when I started writing my reply :)

Atif · Accepted Answer · 2012-12-07 20:27:56Z

1

ok.. i managed it

var tmp_result = {}; // we need this object to make things easy
var result = [];

// add all elements in first array to result, im using this as an object so that I can easily find the keys later
$.each(arOne, function (index, element) {
    tmp_result[element.key] = [element.key, element.value];
});


// loop through second array    
$.each(arTwo, function (index, element) {
    // check if this was key already added
    if (tmp_result[element.key] != undefined) {
        // if it was added earlier then add the new key
        tmp_result[element.key].push(element.value);
    } else {
        // create a new key, add 0 in between since its not there in first array
        tmp_result[element.key] = [element.key, 0, element.value];
    }
});

// now we are left with all those elements which are in first array but not in second
$.each(tmp_result, function (key, element) {
    // check if the array has 3 elements, if not then add 0 in the end since its not there in second one
    if (element.length < 3) element.push(0);
    // pass the flattened out data to result array
    result.push(element);
});

console.log(result);

Fiddle - http://jsfiddle.net/atif089/McfUk/

My output was

[
    ["alpha", 5, 5.5], 
    ["beta", 11, 11.5], 
    ["gamma", 15, 15.5], 
    ["delta", 12, 0], 
    ["epsilon", 55, 0], 
    ["pony", 101, 0], 
    ["psi", 0, 12.5], 
    ["omega", 0, 55.5]
]

answered Dec 7, 2012 at 20:27

Atif

10.9k22 gold badges68 silver badges97 bronze badges

2 Comments

Randy Hall Over a year ago

This is a copy of my answer... except that you create an object then push the object to an array. It's also poor practice to use jQuery (or any library) for functions simple enough accomplish easily without them.

Atif Over a year ago

sorry, I was busy typing the code and didn't look at your answer. Regarding $.each, yes I agree

Mathias · Accepted Answer · 2012-12-07 20:30:27Z

Here is simple take on it. You loop over the first array and push the data into the result array. A Little trickier when you loop over the second. You take each key value pair and check if that key exists in the result array already. If so add it, if not ( found = false ) add it to the result array:

var result = [];
var i;

for ( i = 0; i < arOne.length; i++ ) {
    result.push( [ arOne[ i ].key, arOne[ i ].value ] );
}

for ( i = 0; i < arTwo.length; i++ ) {
    var key = arTwo[ i ].key;
    var value = arTwo[ i ].value;
    var found = false;

    for ( var k = 0; k < result.length; k++ ) {
        if ( result[ k ][ 0 ] === key ) {
            result[ k ].push( value );
            found = true;
        }
    }

    if ( ! found ) {
        result.push( [ key, value ] );
    }

}

result is the array you wanted. Probably not the most efficient way to do it. But it gets the job done.

Also, on a small note. You might want to consider using and object instead of nested arrays. So that your result looks something like this:

var result = {
    alpha: [5, 5.5],  
    beta: [11, 11.5],  
    gamma: [15, 15.5],  
    delta: [12, 0],  
    epsilon: [55, 0],  
    pony: [101, 0],
    psi: [0, 12.5],  
    omega: [0, 55.5], 
}

This might be easier to handle your data later in the code.

Collectives™ on Stack Overflow

Create array where keys match

3 Answers 3

5 Comments

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

5 Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related