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up vote 1 down vote favorite

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 accomplish this - is it possible with a one-liner without explicit variable declaration?

For instance in Java 8 this could have accomplished 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.

share|improve this question
1  
Use Array.prototype.reduce, see MDN for examples. – RobG 30 mins ago
    
@SpencerWieczorek One-liner, without explicit variable declaration, from said criteria it is better. – lexicore 24 mins ago
    
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 22 mins ago
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 20 mins ago
    
Ok, makes sense – Zorgatone 19 mins ago
up vote 6 down vote accepted

You could use Object.assign with computed property names.

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

console.log(object);

share|improve this answer
    
I would prefer Object.assign({}, o, { [a.ds100]: a }) instead of Object.assign(o, { [a.ds100]: a }) to prevent side effects. just a personally preference. – NonPolynomial 18 mins ago
    
the difference is, i return the same object, while NonPolynomial suggest to use a new object all time. – Nina Scholz 15 mins ago
    
@NinaScholz Yes, I got it, thank you. I think it's not really necessary in this case as accumulator object is only used in reduction. – lexicore 7 mins ago

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