...

			function draw(data) {
				svg.selectAll("circle")
					.data(data)
					.enter()
					.append("circle")
					.attr("r", 10)
					.attr("cx", function(x){return xScale(x.weight)})
					.attr("cy", function(x){return yScale(x.height)})
					.style("fill", function(x){return x.colour})
			}

			draw(data);
			
			var data2 = [
				{name: "one", height: 16, weight: 321, colour: "red"},
				{name: "three", height: 25, weight: 330, colour: "blue"},
				{name: "four", height: 21, weight: 777, colour: "purple"},
			];

			alert("wait for it...")

			draw(data2);