Summarize array of objects and calculate average value for each unique object name

arrays, average, javascript, unique

Solution

You'll have to loop through the array, computing the sum and counts for each object. Here's a quick implementation:

function average(arr) {
    var sums = {}, counts = {}, results = [], name;
    for (var i = 0; i < arr.length; i++) {
        name = arr[i].name;
        if (!(name in sums)) {
            sums[name] = 0;
            counts[name] = 0;
        }
        sums[name] += arr[i].value;
        counts[name]++;
    }

    for(name in sums) {
        results.push({ name: name, value: sums[name] / counts[name] });
    }
    return results;
}

Demonstration

Note, this kind of thing can be made much easier if you use a library like Underscore.js:

var averages = _.chain(array)
                .groupBy('name')
                .map(function(g, k) {
                    return { 
                        name: k, 
                        value: _.chain(g)
                                .pluck('value')
                                .reduce(function(x, y) { return x + y })
                                .value() / g.length
                    };
                })
                .value();

Demonstration

Problem

I have an array like so: ``` var array = [ { name: "a", value: 1 }, { name: "a", value: 2 }, { name: "a", value: 3 }, { name: "b", value: 0 }, { name: "b", value: 1 } ]; ``` And I need an array like this: ``` var newarray = [ { name: "a", value: 2 }, { name: "b", value: 0.5 } ] ``` Where the new array has each unique name as an object with the average value. Is there an easy way to accomplish this?

Original source