Using underscore groupby to group an array of cars by their colour

Question

I have an array of cars.

car = {
    make: "nissan",
    model: "sunny",
    colour: "red"
};

How would I use underscore.js to group the array by colour?

I've tried a few combos but I'm not really sure how to specify my iterator condition:

var carsGroupedByColor = _.groupBy(cars, false, colour);
var carsGroupedByColor = _.groupBy(vars, false, function(cars){ return cars[colour]; };

They all return everything in the array each time.

Answer 1

You don't need the false second argument, the following will work:

var redCars = _.groupBy(cars, 'colour');

Note that the second parameter can either be a function or a string. If it's a string Underscore groups by that property name.

Taken from the docs:

Splits a collection into sets, grouped by the result of running each value through iterator. If iterator is a string instead of a function, groups by the property named by iterator on each of the values.

Here's a working example.