Underscore: sortBy() based on multiple attributes

Question

I am trying to sort an array with objects based on multiple attributes. I.e if the first attribute is the same between two objects a second attribute should be used to comapare the two objects. For example, consider the following array:

var patients = [
             [{name: 'John', roomNumber: 1, bedNumber: 1}],
             [{name: 'Lisa', roomNumber: 1, bedNumber: 2}],
             [{name: 'Chris', roomNumber: 2, bedNumber: 1}],
             [{name: 'Omar', roomNumber: 3, bedNumber: 1}]
               ];

Sorting these by the roomNumber attribute i would use the following code:

var sortedArray = _.sortBy(patients, function(patient) {
    return patient[0].roomNumber;
});

This works fine, but how do i proceed so that 'John' and 'Lisa' will be sorted properly?

Answer 1

sortBy says that it is a stable sort algorithm so you should be able to sort by your second property first, then sort again by your first property, like this:

var sortedArray = _(patients).chain().sortBy(function(patient) {
    return patient[0].name;
}).sortBy(function(patient) {
    return patient[0].roomNumber;
}).value();

When the second sortBy finds that John and Lisa have the same room number it will keep them in the order it found them, which the first sortBy set to "Lisa, John".