compare sentences / equality fitness function

compareSentences

function calculateStringFitness(str0,str1,opt){

	function countMatches(a0, a1){
		var matches, pos0, pos1, matchObj;
		matches = pos0 = pos1 = 0;
		matchObj = {};

		a0 = a0.sort();
		a1 = a1.sort();

		function compareToSortOrder( a, b ) {
			if(a===b) return 0;
			return ([a,b].sort()[0]===a) ? -1 : 1;
		}

		do {
			var compare = compareToSortOrder( a0[pos0], a1[pos1] );
			if (compare == 0) {
				matchObj[a0[pos0]] = (matchObj[a0[pos0]]) ? matchObj[a0[pos0]]+1 : 1;
				matches++; pos0++; pos1++;
			}
			else if (compare < 0) pos0++;
			else if (compare > 0) pos1++;
		} while ( pos0 < a0.length && pos1 < a1.length );

		return {
			matchCount:matches,
			matches:matchObj
		}
	}

	function sorensenDice(str0, str1, opt){
		if(opt && opt.caseSensitive == false){
			str0 = str0.toLowerCase();
			str1 = str1.toLowerCase();
		}
		var splitChar = (opt && opt.split == 'word') ? ' ':'';
		var a0 = str0.split(splitChar);
		var a1 = str1.split(splitChar);
		var match = countMatches(a0, a1);
		var dsc = (2.0*(match.matchCount))/(a0.length+a1.length);
		return {
			matchCount: match.matchCount,
			matches: match.matches,
			simFactor: dsc
		};
	}
	// calculate sorensenDice aka match coefficient
	// https://en.wikipedia.org/wiki/S%C3%B8rensen%E2%80%93Dice_coefficient
	var sd = sorensenDice(str0,str1,opt);
	// calculate jaccardIndex from sorensenDice aka overlap coefficient
	// https://en.wikipedia.org/wiki/Jaccard_index
	var ji = sd.simFactor/(2-sd.simFactor);

	return {
		matchCount: sd.matchCount,
		matches: sd.matches,
		sorensenDice: sd.simFactor,
		jaccardIndex: ji
	};
}