JavaScript Objects - Arrays

Question

If I have an Array with years Y=[2014, 2011, 2010, 2013, 2014, 2007, 2004], and if I want to group these years for n and make object like this (n=3 lets say):

property name is min(Y) - (min(Y)+3), property value: average like (min(Y) + (min(Y)+3))/2).

obj={"2004-2007": "2005.5", "2008-2011":"2009.5", "2012-2015": "2013.5"}

Further, I would later like to be able to get my average value, so if I ask for 2009 i get the value of group in which this element belong, or 2009.5.

Is it possible? Probably there is a better way? I don't care how object looks, I would just like to get my group average value when I ask for it.

Answer 1

Assume the grouping is based on continuous year instead of every 4 of the year in data list, i.e even there is no data for year 2016-2019, there is still a group for it.

function GroupedAvgData(dataList, groupSize){
    //get the min(Y) for a given year
    function getMinY(year, minYear){
        var gap = year - minYear;
        return minYear + gap - gap%groupSize;
    }

    //build a groups with minY as key and average as value
    function buildGrouping(sortedDataList, groupSize){
        var currentMin=0, currentSum=0, currentCount=0, groups={};
        for(var i=0,len=sortedDataList.length; i<len;i++){
            var minY = getMinY(sortedDataList[i], sortedDataList[0]);
            if(currentMin != minY){
                if(currentCount > 0){
                    groups[currentMin] = currentSum / currentCount;
                }
                currentCount = 1;
                currentMin = minY;
                currentSum = sortedDataList[i];
            }else{
                currentSum += sortedDataList[i];
                currentCount++;
            }
            if( i == len - 1 && currentCount>0){
                groups[currentMin] = currentSum / currentCount;
            }
        }
        return groups;
    }
    this.sortedList = dataList.sort(function(a,b){return a - b;});
    this.groups = buildGrouping(this.sortedList, groupSize);
    this.groupSize = groupSize; 
}

GroupedAvgData.prototype.getAverageForYear = function(year){
    var gap = year - this.sortedList[0];
    if(gap >= 0){
        var minY = this.sortedList[0] + (gap-gap%this.groupSize);
        if(this.groups[minY]){return this.groups[minY];}
    }
    return 0;
}

To use it, i.e. query the average for some year:

var Y=[2014, 2011, 2010, 2013, 2014, 2007, 2004];
var myAvg = new GroupedAvgData(Y, 4);
console.log(myAvg.getAverageForYear(2009));