I'd like to convert an array into an object using one of the properties as key.

For instance:

var stations = [ { name: 'A Coruna', ds100: 'OECSC' }, ... ];

I'd like to get stationByDs100:

{ 'OECSC': { name: 'A Coruna', ds100: 'OECSC' }, ... }

At the moment I do it as follows:

var stationByDs100 = {};
stations.forEach(station => stationByDs100[station.ds100] = station);

I'm looking for a better way to acplish this - is it possible with a one-liner without explicit variable declaration?

For instance in Java 8 this could have acplished with streams and collectors in one line like:

Map<String, Station> stationByDs100 = stations.stream()
    .collect(toMap(Station::getDs100, identity()));

So I was thinking maybe there's a similar way in JS.

I'm using Node.js so OK to use the latest JS/ES features Node.js supports.

I've browsed through a rougly dozen existing answers but they mostly use older JS/ES versions and suggest even longer solutions.

I'd like to convert an array into an object using one of the properties as key.

For instance:

var stations = [ { name: 'A Coruna', ds100: 'OECSC' }, ... ];

I'd like to get stationByDs100:

{ 'OECSC': { name: 'A Coruna', ds100: 'OECSC' }, ... }

At the moment I do it as follows:

var stationByDs100 = {};
stations.forEach(station => stationByDs100[station.ds100] = station);

I'm looking for a better way to acplish this - is it possible with a one-liner without explicit variable declaration?

For instance in Java 8 this could have acplished with streams and collectors in one line like:

Map<String, Station> stationByDs100 = stations.stream()
    .collect(toMap(Station::getDs100, identity()));

So I was thinking maybe there's a similar way in JS.

I'm using Node.js so OK to use the latest JS/ES features Node.js supports.

I've browsed through a rougly dozen existing answers but they mostly use older JS/ES versions and suggest even longer solutions.

• javascript
• node.js

Share Improve this question Follow asked Jan 29, 2017 at 10:09 lexicorelexicore 43.7k1717 gold badges140140 silver badges225225 bronze badges 5

• 1 Use Array.prototype.reduce, see MDN for examples. – RobG Commented Jan 29, 2017 at 10:11
• @SpencerWieczorek One-liner, without explicit variable declaration, from said criteria it is better. – lexicore Commented Jan 29, 2017 at 10:17
• Is there a specific purpose for wanting the code to be a one-liner? Usually one-line code, especially involving functional-style array methods, are slower than the equivalent code using for/while loops and more than one line of code – Zorgatone Commented Jan 29, 2017 at 10:19
• 1 @Zorgatone No technical reason. I don't care about performance in this case and wanted to learn more about functional style in JS as I'm quite weak in that. – lexicore Commented Jan 29, 2017 at 10:21
• Ok, makes sense – Zorgatone Commented Jan 29, 2017 at 10:22

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2 Answers 2

Sorted by: Reset to default 9

You could use Object.assign with puted property names.

var stations = [ { name: 'A Coruna', ds100: 'OECSC' }],
    object = stations.reduce((o, a) => Object.assign(o, { [a.ds100]: a }), {});

console.log(object);

Object.fromEntries can help with this:

const stations = [{ name: 'Berlin Südkreuz', ds100: 'BPAF' }, { name: 'Berg', ds100: 'KBEG' }];
const object = Object.fromEntries(stations.map(o => [o.ds100, o]));
console.log(object);