Concat n numbers of array into a single array

Question

Suppose i have an object whose values are arrays just like this:

obj = {
    'key1': [1,2],
    'key2': [3,4],
    'key3': [5,6],
}

How to i merge all the arrays of the object into one using concat. The number of keys of the object is dynamic of course but it will have at least one instance The desired output is this:

[1,2,3,4,5,6]

Yevhen Horbunkov · Accepted Answer · 2020-03-24 22:05:51Z

9

flat() on Object.values() is supposed to do the job:

const obj = {
        key1: [1,2],
        key2: [3,4],
        key3: [5,6]
      },
      merged = Object.values(obj).flat()

console.log(merged)

.as-console-wrapper{min-height:100%}

If being unlucky enough to deal with IE or Edge, one may fallback to reduce() for flattening:

const obj = {
        key1: [1,2],
        key2: [3,4],
        key3: [5,6]
      },
      merged = Object.keys(obj).reduce(function(r,k){     
        return r.concat(obj[k])
      }, [])

console.log(merged)

.as-console-wrapper{min-height:100%}

edited Mar 24, 2020 at 22:05

answered Dec 11, 2019 at 13:40

Yevhen Horbunkov

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2 Comments

Gup3rSuR4c Over a year ago

Or flatMap, I think flat works on arrays only, but he has an object with array properties.

briosheje Over a year ago

Beware of flat support though. Worth mentioning that, in my opinion.

Mathew Berg · Accepted Answer · 2019-12-11 13:40:25Z

4

var obj={ 'key1': [1,2], 'key2': [3,4], 'key3': [5,6] };

var result = Object.values(obj)
    .reduce((accum, values) => {
        accum.push(...values);
        return accum;
    }, []);

console.log(result);

answered Dec 11, 2019 at 13:40

Mathew Berg

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4 Comments

Mathew Berg Over a year ago

@Yevgens answer is better.

Giovani Vercauteren Over a year ago

This answer has better broswer support though, so if for some reason OP needs to support IE and/or Edge this answer would be the correct one.

jtwalters Over a year ago

If we consider IE we must replace the spread operator ... to concat() so the result can be return accum.concat(values);

ggorlen Over a year ago

Or [].concat(...Object.values(obj)) and skip reduce entirely.

jtwalters · Accepted Answer · 2019-12-11 13:42:42Z

2

If you assume all the values of the object will an array you can make a Object.values() loop and concat each array.

const obj={
    'key1': [1,2],
    'key2': [3,4],
    'key3': [5,6],
};

const res = [];
for (const value of Object.values(obj)) {
    res.push(...value);
}
/// res: [1,2,3,4,5,6]

answered Dec 11, 2019 at 13:42

jtwalters

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