Groups given object by a key

code.js

var events = data.events;
var date = {};
for (var i = 0, ii = events.length; i < ii; i++) {
    if (!date[events[i]['date']]) {
        date[events[i]['date']] = [];
    };
    date[events[i]['date']].push(events[i]);
}

console.log(date);

data.js

var data = {
    events: [
        {
            id: 1,
            date: '1/1/2011'
        },
        {
            id: 2,
            date: '1/1/2011'
        },
        {
            id: 3,
            date: '2/1/2011'
        },
        {
            id: 4,
            date: '2/1/2011'
        },
        {
            id: 5,
            date: '2/1/2011'
        },
        {
            id: 6,
            date: '3/1/2011'
        },
        {
            id: 7,
            date: '3/1/2011'
        },
        {
            id: 8,
            date: '4/1/2011'
        }
    ]
};