create array of values with same key from an array of objects

Question

I have an array of objects that looks like this:

[
     {
      key1: val_1.a
      key2: val_2.a
      key3: val_3.a
     },{
      key1: val_1.b
      key2: val_2.b
      key3: val_3.b
     },{
      key1: val_1.c
      key2: val_2.c
      key3: val_3.c
     }
]

I want to use that object to create another object that looks like this:

{ 
    key1: [val_1.a, val_1.b, val_1.c]
    key2: [val_2.a, val_2.b, val_2.c]
    key3: [[val_3.a, val_3.b, val_3.c]
}

Since the keys are the same in each object I just want to save in an array all the values that correspond to each key.

Please, If there is anyone who have had to do this before and could share the code it would be great. Thanks in advance.

jfriend00 · Accepted Answer · 2014-11-12 23:17:48Z

You can do it like this in a way that will work in all browsers and will even work if all objects don't have the exact same set of keys (e.g. it will just accumulate data for whatever keys exist):

function combineKeyData(data) {
    var output = {}, item;
    // iterate the outer array to look at each item in that array
    for (var i = 0; i < data.length; i++) {
        item = data[i];
        // iterate each key on the object
        for (var prop in item) {
            if (item.hasOwnProperty(prop)) {
                // if this keys doesn't exist in the output object, add it
                if (!(prop in output)) {
                    output[prop] = [];
                }
                // add data onto the end of the key's array
                output[prop].push(item[prop]);
            }
        }
    }
    return output;
}

Working jsFiddle: http://jsfiddle.net/jfriend00/0jjquju9/

Explanation:

For each item in the array
For each key in an item in the array
Add the key as an empty array to the output object if it doesn't already exist
Add the data onto the end of the array for that key in the output object
Return the resulting new object

Barmar · Accepted Answer · 2014-11-12 23:10:25Z

1

result = {};
for (var i = 0; i < array.length; i++) {
    var obj = array[i];
    for (var key in obj) {
        if (obj.hasOwnProperty(key)) {
            if (result[key]) {
                result[key].push(obj[key]);
            } else {
                retult[key] = [obj[key]];
            }
        }
    }
}

answered Nov 12, 2014 at 23:10

Barmar

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Comments

Madara's Ghost · Accepted Answer · 2014-11-12 23:28:05Z

0

var arr = [
 {
  key1: 'val_1.a',
  key2: 'val_2.a',
  key3: 'val_3.a'
 },{
  key1: 'val_1.b',
  key2: 'val_2.b',
  key3: 'val_3.b'
 },{
  key1: 'val_1.c',
  key2: 'val_2.c',
  key3: 'val_3.c'
 }
]

var result = arr.reduce(function(obj, current) { //Reduce the array to an object
    Object.keys(current).forEach(function(key) { //Each key
        obj[key] = obj[key] || []; //Has to be an array if not exists
        obj[key] = Array.isArray(obj[key]) ? obj[key] : [obj[key]]; //Has to be an array if not an array
        obj[key].push(current[key]); //Add current item to array of matching key
    });
    return obj; //Continue to the next object in the array
});

console.log(result);

The above functions: Array#reduce, Array#forEach, Array.isArray, Object.keys are all part of the ECMAScript 5 specifications, as a result, they are not available in IE8 and below.

edited Nov 12, 2014 at 23:28

answered Nov 12, 2014 at 23:10

Madara's Ghost

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5 Comments

Barmar Over a year ago

This returns a 2-dimensional array, he wants an object containing arrays.

jfriend00 Over a year ago

This also assumes that all objects in the original array have exactly the same set of keys - no more no less. That's a shortcut that is true for the OP's exact data, but isn't the safest way to build the output data structure.

Madara's Ghost Over a year ago

@jfriend00 And now it doesn't anymore.

Barmar Over a year ago

If the result is going to make sense, it seems like that might be a necessity. Otherwise, the correspondence between the elements in the resulting sub-arrays will be wrong.

Zvezdas1989 Over a year ago

This is not good. What is value is null for example. You should your CODE op.

Rohan Kumar · Accepted Answer · 2017-05-05 08:22:14Z

0

let R = require('ramda');
let arr =[
    {
     'key1': 'a',
     'key2': 'b',
     'key3': 'c',
    },{
     'key1': 'a1',
     'key2': 'b1',
     'key3': 'c1',
    },{
     'key1': 'a2',
     'key2': 'b2',
     'key3': 'c2',
    }
];

let key1 = R.pluck('key1', arr);
let key2 = R.pluck('key2', arr);
let key3 = R.pluck('key3', arr);
let obj = {
     key1,
     key2,
     key3
};

Obj = { key1: [ 'a', 'a1', 'a2' ], key2: [ 'b', 'b1', 'b2' ], key3: [ 'c', 'c1', 'c2' ] }

edited May 5, 2017 at 8:22

Rohan Kumar

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answered Aug 23, 2016 at 12:56

Rose

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1 Comment

Brynden Over a year ago

Perhaps you could explain your proposed solution, rather than just posting some code? - Found in review.

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