https://gist.github.com/3914319
gistfile1.coffee
# Group by field1 and field2
groupedData = _.groupBy(data, (d) ->
"#{d.field1}-#{d.field2}"
)
groupby.js
// Group by field1 and field2
var groupedData = _.groupBy(data, function(d) {
return d.field1 + "-" + d.field2;
});