Mapping

JavaScript

var playLog = ['Madonna', 'Madonna', 'Prince', 'Pearl Jam', 'Madonna', 'Pearl Jam', 'Metallica', 'Prince', 'Klaus Wunderlich', 'Pontiac', 'Madonna'];

var topList = playLog.map(function(artist){
		// first we want to establish the format for the resulting object
		
		var obj = {
		artist : artist , 
		playCount : 1
		};
		
		return obj;
		
	});
	
console.log(topList);