gistfile1.txt

function Map() {

	emit(
		{ClientVersion:this.ClientVersion, PublisherId:this.PublisherId},				// how to group
		{SessionCount: 1, userIds:[this.UserId]}	// associated data point (document)
	); 
	
}

function Reduce(key, values) {

	var reduced = {SessionCount:0,userIds:{}}; // initialize a doc (same format as emitted value)
	values.forEach(function(val) {
		reduced.SessionCount += val.SessionCount; 	// reduce logic
		val.userIds.forEach(function(uid){
		if(!reduced.userIds[uid]){
			reduced.userIds[uid]=true;
			}
			});
		
	});

	return reduced;	
	
}

function Finalize(key, reduced) {
	return {UserCount:reduced.userIds.length, SessionCount:reduced.SessionCount};
}