How to use groupBy in Backbone.js to group collections?

Question

An example collection (showing models only):

[
    {
        name: "Bob"
        date: "Thu Mar 29 2012"
    },
    {
        name: "James"
        date: "Fri Mar 30 2012"
    },
    {
        name: "Dylan"
        date: "Fri Mar 30 2012"
    },
    {
        name: "Stanley"
        date: "Sat Mar 31 2012"
    },
]

How can I use Underscore.js' groupBy function to group models with the same date?

Answer 1

If you are grouping an actual backbone collection you can use the backbone method groupBy which implicitly uses underscore _.groupBy functionality. This is a much cleaner approach in my opinion.

collection.groupBy( function(model){
  return model.get('date');
});

Answer 2

ThiefMaster answer is perfectly valid, but it caused me some confusion because I was searching a solution for a backbone.js collection as the title indicates.

If the question object is a backbone collection we should do the following to group the models by date:

_.groupBy(collection.models, function(model){
    return model.get('date')
});

I hope it helps

Answer 3

Use _.groupBy(data, 'date');

You could also use pass a custom function, but in this case it's not necessary as the attribute shortcut syntax above works fine.

_.groupBy(data, function(row) {
    return row.date;
});

Demo:

> _.groupBy(data, 'date')
{ 'Thu Mar 29 2012': [ { name: 'Bob', date: 'Thu Mar 29 2012' } ],
  'Fri Mar 30 2012':
   [ { name: 'James', date: 'Fri Mar 30 2012' },
     { name: 'Dylan', date: 'Fri Mar 30 2012' } ],
  'Sat Mar 31 2012': [ { name: 'Stanley', date: 'Sat Mar 31 2012' } ] }
> _.groupBy(data, function(row) { return row.date });
{ 'Thu Mar 29 2012': [ { name: 'Bob', date: 'Thu Mar 29 2012' } ],
  'Fri Mar 30 2012':
   [ { name: 'James', date: 'Fri Mar 30 2012' },
     { name: 'Dylan', date: 'Fri Mar 30 2012' } ],
  'Sat Mar 31 2012': [ { name: 'Stanley', date: 'Sat Mar 31 2012' } ] }
>