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var margin = {top: 30, right: 0, bottom: 30, left: 50},
    width = 210 - margin.left - margin.right,
    height = 210 - margin.top - margin.bottom;

//Read the data
d3.csv("https://raw.githubusercontent.com/holtzy/data_to_viz/master/Example_dataset/5_OneCatSevNumOrdered.csv", function(data) {

  // group the data: I want to draw one line per group
  var sumstat = d3.nest() // nest function allows to group the calculation per level of a factor
    .key(function(d) { return d.name;})
    .entries(data);

