D3.js group chart

HTML

<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<div id="chart"></div>

CSS

* {
  margin: 0;
  padding: 0;
  border: 0;
}

body {
  background: #ffd;
}

.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 1.5px;
}

JavaScript

//https://bl.ocks.org/andrew-reid/64a6c1892d1893009d2b99b8abee75a7

//("%m/%d/%Y %H:%M:%S %p")("1/2/2014 8:22:05 AM")
var $this =  $('#chart');

w = 960;
h = 500;

var data = [{
  "date": "09:00:00",
  "Monday": 18.0,
  "Tuesday": 28.8,
  "Wednesday": 8.8,
  "Thursday": 3.03,
  "Friday": 8.8,
  "Saturday": 3.8,
  "Sunday": 12.8
}, {
  "date": "10:00:00",
  "Monday": 33.3,
  "Tuesday": 12.8,
  "Wednesday": 18.8,
  "Thursday": 43.03,
  "Friday": 38.8,
  "Saturday": 68.8,
  "Sunday": 79.8
}, {
  "date": "11:00:00",
  "Monday": 35.7,
  "Tuesday": 56.8,
  "Wednesday": 34.8,
  "Thursday": 23.03,
  "Friday": 138.8,
  "Saturday": 58.8,
  "Sunday": 59.8
}, {
  "date": "12:00:00",
  "Monday": 33.7,
  "Tuesday": 53.8,
  "Wednesday": 24.8,
  "Thursday": 13.03,
  "Friday": 128.8,
  "Saturday": 18.8,
  "Sunday": 19.8
}, {
  "date": "13:00:00",
  "Monday": 43.7,
  "Tuesday": 33.8,
  "Wednesday": 24.8,
  "Thursday": 123.03,
  "Friday": 138.8,
  "Saturday": 28.8,
  "Sunday": 39.8
}, {
  "date": "14:00:00",
  "Monday": 235.7,
  "Tuesday": 156.8,
  "Wednesday": 134.8,
  "Thursday": 123.03,
  "Friday": 138.8,
  "Saturday": 158.8,
  "Sunday": 159.8
}, {
  "date": "15:00:00",
  "Monday": 125.7,
  "Tuesday": 126.8,
  "Wednesday": 234.8,
  "Thursday": 123.03,
  "Friday": 228.8,
  "Saturday": 158.8,
  "Sunday": 259.8
}, {
  "date": "16:00:00",
  "Monday": 25.7,
  "Tuesday": 46.8,
  "Wednesday": 54.8,
  "Thursday": 33.03,
  "Friday": 18.8,
  "Saturday": 48.8,
  "Sunday": 39.8
}, {
  "date": "17:00:00",
  "Monday": 2.7,
  "Tuesday": 4.8,
  "Wednesday": 3.8,
  "Thursday": 3.03,
  "Friday": 8.8,
  "Saturday": 38.8,
  "Sunday": 19.8
}];

var yLabel = "Count";


var svg = d3.select($this[0]).append("svg"),
  margin = {
    top: 20,
    right: 20,
    bottom: 30,
    left: 40
  },
  width = w - margin.left - margin.right,
  height = h - margin.top - margin.bottom,
  g = svg
  .attr("width", w)
  .attr("height", h)
  .append("g")
  .attr("transform", "translate(" + margin.left + "," + margin.top...