compress.js

// function for "compressing" array data into a shorter array whilst maintaining
// the same cross-total value and relativity of values to each other
function compressArrayData (arr, toLen) {
	if (!Array.isArray(arr) || isNaN(toLen) || arr.length < toLen) throw "ArgumentError";
	// 1 new data field is equals to this many source fields
	var sizeRatio = arr.length / toLen;
	// result storage
	var results = [];
	var resIndx = 0;
	// rest from previous source iteration
	var rest = 0;
	// ratio after previous source iteration
	var lastRatio = sizeRatio;
	// value carry over
	var lastVal = 0;
	for (var i = 0; i < arr.length; i++) {
		// get rest local and reset it
		var r = rest;
		rest = 0;
		// current value
		var v = arr[i];
		// check if the current value needs to be splitted
		if (lastRatio < 1) {
			var c = v * lastRatio;
			rest = v - c;
			v = c;
		}
		// decrement next source ratio for each iteration
		lastRatio -= 1;
		// store the current value
		lastVal += v + r;
		// ratio reached => insert value & add next ratio
		if (lastRatio <= 0) {
			results[resIndx++] = lastVal;
			lastVal = 0;
			lastRatio += sizeRatio;
		}
	}
	return results;
}

// e.g. this
var test = [ 1, 0.5, 0.2, 0.5, 1 ]; //sum 3.2

// becomes this
// [ 1.125, 0.475, 0.475, 1.125 ] sum 3.2
var compressd = compressArrayData(test, 4);