 dimensions and margins of the graph
const 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").then( function(data) {

  // group the data: I want to draw one line per group
  const sumstat = d3.group(data, d => d.name) // nest function allows to group the calculation per level of a factor