Map Reduce using UnderscoreJS

Question

I am trying to convert the following dataset:

var foo = {
        "2011":
            [{ "date": "2011-08-01T00:00:00", "y": "100" },
             { "date": "2011-08-05T00:00:00", "y": "400" },
             { "date": "2011-09-01T00:00:00", "y": "900" }
            ],
        "2012": 
           [{ "date": "2012-07-22T00:00:00", "y": "200" },
            { "date": "2012-09-22T00:00:00", "y": "430" },
            { "date": "2012-10-26T00:00:00", "y": "100" }
           ]
       }

into something like this:

var foo1 = {
        "2011":
            [{ "y": "1400" }],
        "2012": 
            [{ "y": "730" }]
       }

What would be the best way to do this using UnderscoreJS? Thanks in advance!

Trying to render several reports client-side in a dashboard and need to be able to modify the dataset without having to make repeated server calls for each report. — user3683545
– user3683545, Commented May 28, 2014 at 12:22

Bergi · Accepted Answer · 2014-05-28 12:58:38Z

1

Underscore does not have a utility for object mapping unfortunately. We'd have to emulate that with _.object(_.keys(…), _.map(_.values(…), …)) or by _.cloneing the object, iterating it by _.each and manually assigning. Let's better extend the lib to get more readable code:

_.mixin({
    mapObject: function(obj, iterator, context) {
        return _.each(_.clone(obj), function(items, p, o) {
             o[p] = iterator.apply(this, arguments);
        }, context);
    }
});

var foo1 = _.mapObject(foo, function(items) {
    return [{y: _.reduce(_.map(_.pluck(items, "y"), Number), function(m, y) {
         return m + y;
    }, 0) }];
});

edited May 28, 2014 at 12:58

answered May 28, 2014 at 12:27

Bergi

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3 Comments

Bergi Over a year ago

Just what the OP wanted: a map and a reduce (though not a map-reduce). Better now with the helper function?

Henrik Andersson Over a year ago

I was trying to make a joke, but no, it's still to me, totally unreadable but it works and feels overly complicated just because it's underscore, but correct nonetheless.

Bergi Over a year ago

Please, come up with an easier solution, I'd appreciate it :-) I've further simplified it, now using an actual map-reduce. More readable now?

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