How to group by 15 minutes interval a json collection in Javascript

Starting with the UnderscoreJS code from tjdett for a group-by-year question:

var dateGroups = _.chain(objarray)
                  .groupBy(function(obj) { return obj.date.getFullYear(); })
                  .sortBy(function(v, k) { return k; })
                  .value();

You could try this same solution with a groupBy function designed for 15 minute intervals instead of years, with return Math.floor(+(obj.date)/(1000*60*15)); This return statement uses + to convert the Date object to a number of milliseconds (since epoch), and then divides by 1000*60*15 for 15 minute intervals with Math.floor() discarding the fraction.

For that to work, obj.date must be type Date. If your dates are just strings, you may first need to parse the year, month, day, hour, minutes out of those strings and then construct a new Date object.

This will create absolute 15 minute clock blocks, i.e. 01:00:00-01:14:59.9999, 01:15:00-01:29:59.9999; not 15 minutes that begin with new activity.

So if you want a group of 15 minutes of data that starts with new data, the groupBy function would need to be created with a closure retaining state of when the current group ends so that new groups could be started, and it would need to be fed from objects sorted by date, so that a sort needs to happen first.

That sounds Rube-Goldbergish, and might be easier to do directly like this (untested):

fixDates(objArray); // a function you'll write to turn your date strings into Date objects
function compareDates(a,b){ return (+a.date)-(+b.date); }
objArray.sort(compareDates); // sorts in place, array is changed
var groups = [], g=[], d=0;
for (var gx=+objArray[0].date+15*60*1000,i=0,l=objArray.length; i<l; ++i){
    d = +(objArray[i].date);
    if (d>gx){ 
       groups.push(g);
       g = [];
       gx = +objArray[i].date+15*60*1000;
    }
    g.push(objArray[i]);
}
groups.push(g);  // include last group otherwise unpushed
// result in groups

This method takes startDate,EndDate and interval to break DateTime and return DateTime Collection on specified interval

   const createDateTimeInterval = (startDate, endDate, interval) => {
        const dateArray = [];
        let currentDate = new Date(startDate);
        while (currentDate < new Date(endDate)) {
            var date = new Date(currentDate);
            let dateinString;
            if (date.getHours() < 12) {
                dateinString = (date.getHours() < 10 ? '0' + date.getHours() : date.getHours()) + ':' + (date.getMinutes() === 0 ? date.getMinutes() + '0' : date.getMinutes()) + ' AM';
            }
            else {
                dateinString = ((date.getHours() - 12) < 10 ? '0' + (date.getHours() - 12) : (date.getHours() - 12)) + ':' + (date.getMinutes() === 0 ? date.getMinutes() + '0' : date.getMinutes()) + ' PM';
            }
            dateArray.push({ label: dateinString, value: JSON.stringify(new Date(currentDate)) });
            currentDate = new Date(currentDate.getTime() + interval);
        }
    
        return dateArray;
    }
    const currentDate = new Date(new Date().getFullYear() + '-' + new Date().getMonth() + '-' + new Date().getDate())
    const nextDate = new Date(new Date(currentDate).getTime() + 60000 * 60 * 24)

This is the 15 minutes interval on a current date.

var dateOptions = createDateTimeInterval(currentDate, nextDate, (60000 * 15));