function drawRain() {
svg.append("g")
.call(xAxis);
svg.append("g")
.call(yAxis)
.selectAll("text")
.attr("x", width / 2)
.attr('transform', 'translate(0, 10)')
.style("font", "18px times");
let circles = svg.selectAll('circle')
.data(data)
.enter().append('circle')
.attr('cx', (d, i) => x(i))
.attr('cy', margin.top)
.attr('r', 5)
.attr('fill', 'firebrick')
circles.transition()
.delay((d, i) => 100 * i)
.duration(1000)
.ease(d3.easeBounce)
.attr('cy', d => y(d.group) + y.bandwidth() / 2)
return svg.node();
}