anchor.diff:  
       // Add the line
       line.append("path")
  -      .datum(data)
  +      .datum(word_count_data)
         .attr("class", "line")  // I add the class line to be able to modify this line later on.
         .attr("fill", "none")
         .attr("stroke", "steelblue")
  
positive.code: 
      // Add Y axis
      var y = d3.scaleLinear()
        .domain([0, d3.max(data, function(d) { return +d.value; })])
        .range([ height, 0 ]);
      yAxis = svg.append("g")
        .call(d3.axisLeft(y));
  
negative.code: 
      // If user double click, reinitialize the chart
      svg.on("dblclick",function(){
        x.domain(d3.extent(word_count_data, function(d) { return d.sentence_index; }))
        xAxis.transition().call(d3.axisBottom(x))
        line
          .select('.line')
  