Question

Only just introduced to _Underscore so this may be totally nonsense but I’m wondering if the library can indeed do what I want.

I have an object containing 5 items:

Name, v2007,v2008,v2009,v2010

I simply want to go through the entire object and get the SUM of each distinct value in Name (much similar to SQL’s GroupBy and SUM).

I have the following:

var distincts = [];
$.each(tmp, function (key, value) {
    $.each(value, function (fieldName, fieldValue) {
        if (fieldName == 'Name') {
            if ($.inArray(fieldValue, distincts) == -1) {
                distincts.push(fieldValue);
            }
        }
    });
});

$.each(distincts, function (a, b) {
    var t = _.where(tmp, {Name: b});
    var sum = _.reduce(t.v2007, function (memo, num) {
        return memo + num;
    }, 0)
    console.log(sum);
});

Which is returning 0 all the time, in fact I’m not sure how to retrieve a SUM of fields v2011, v2013 other than hard-coding them in which is simply not practical!

Can someone help me a little here, is there a simple way of getting the _Underscore library to SUM all fields (that, say, start with ‘v’) based on a Group of the Name?

Answer 1

I think this does what you want:

var groups = _.groupBy(function(name) { return name.charAt(0) });
var sums = _.map(groups, function(group) {
    return _.reduce(group, function (a, b) { return a+b; }, 0);
});