javascript underscorejs group and sum data

Question

I have a data like this:

var dates = [
    {date: "2000-01-01", total: 120}, 
    {date: "2000-10-10", total: 100}, 
    {date: "2010-02-08", total: 100},
    {date: "2010-02-09", total: 300}
];

I want to create a grouped and sum of total like this.

var grouped = [
    {date: "2000", total: 220}, 
    {date: "2010", total: 100}
];

I am using underscorejs but did not find function.

var byYear = _.map(dates, function(item){ 
    var year = new Date(Date.parse(item.date)).getFullYear();

    return {date: year, total: item.total}; 
});

workig code is here.

ad77 · Accepted Answer · 2014-08-11 08:21:11Z

Using the reduce function. I see this has been jst answered before i could post. But just spent time coding it. So posting it here anyways. Btw this answer uses chaining.

var byYear = _.chain(dates)
            .map(function(item){ 
                var year = new Date(Date.parse(item.date)).getFullYear();
                return {date: year, total: item.total}; 
            })
            .groupBy('date')
            .map(function (value,key) { 
                            var reduceVal = _.reduce(value, function (acc, val)
                                                            { 
                                                                return acc + val.total;
                                                            },0 ); 
                            return {'year':key,'total' :reduceVal};
                })
            .value();


alert(JSON.stringify(byYear));

Alex Kiselev · Accepted Answer · 2014-08-11 07:58:53Z

1

I believe you are looking for the reduce function:

var dates = [
    {date: "2000-01-01", total: 120}, 
    {date: "2000-10-10", total: 100}, 
    {date: "2010-02-08", total: 100}
];

var byYear = _.map(dates, function(item){ 
    var year = new Date(Date.parse(item.date)).getFullYear();        
    return {date: year, total: item.total}; 
});

var grouped = _.reduce(byYear, function(memo, item) {
    memo[item.date] = (memo[item.date] || 0) + item.total;
    return memo;
}, {});

answered Aug 11, 2014 at 7:58

Alex Kiselev

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