Summarise data using .countBy
Try this:
var data =
[
{"id":"338b79f07dfe8b3877b3aa41a5bb8a58","value":{"country":"United States"}},
{"id":"338b79f07dfe8b3877b3aa41a5bb983e","value":{"country":"Norway"}},
{"id":"338b79f07dfe8b3877b3aa41a5ddfefe","value":{"country":"Hungary"}},
{"id":"338b79f07dfe8b3877b3aa41a5fe29d7","value":{"country":"United States"}},
{"id":"b6ed02fb38d6506d7371c419751e8a14","value":{"country":"Germany"}},
{"id":"b6ed02fb38d6506d7371c419753e20b6","value":{"country":"Hungary"}},
{"id":"b6ed02fb38d6506d7371c419755f34ad","value":{"country":"United States"}},
{"id":"b6ed02fb38d6506d7371c419755f3e17","value":{"country":"Germany"}},
{"id":"338b79f07dfe8b3877b3aa41a506082f","value":{"country":"United Kingdom"}},
{"id":"9366afb036bf8b63c9f45379bbe29509","value":{"country":"United Kingdom"}}
];
var countData = _.countBy(data, function(obj){
return obj.value.country.replace(" ", "_");
});
console.log(countData);
JSFiddle: http://jsfiddle.net/hyDv7/1/