summarize active and total browsers by its names

summary-through-tuples.es6

var summary = hubs => _(hubs)
    .groupBy('browserName')
    .mapValues((data, bro) =>
        _(data).mapTuple(['active', 'total']).sumTuple().value()
    )
    .value();

var hubs = [{
  host: 'hub01',
  browserName: 'firefox',
  active: 3,
  total: 10
}, {
  host: 'hub02',
  browserName: 'chrome',
  active: 2,
  total: 5
}, {
  host: 'hub03',
  browserName: 'firefox',
  active: 0,
  total: 10
}];

_.mixin({
    mapTuple: (arr, props) => {
        return _.map(arr, item => {
            return _.pick(item, props);
        })
    },
    sumTuple: collection => {
        let init = _.mapValues(collection[0], _.constant(0));

        return _.reduce(collection, (sum, tuple) => {
            _.forEach(tuple, (item, key) => sum[key] += item);
            return sum;
        }, init);
    }
});

summary(hubs);