title: Stacked area chart data with NaN
body: <p>I have a demo here 
  <a href="https://stackblitz.com/edit/stacked-area-basic?file=src/app/bar-chart.ts" rel="nofollow noreferrer">https://stackblitz.com/edit/stacked-area-basic?file=src/app/bar-chart.ts</a></p>
  
  <p>I'm trying to create a stacked area chart. This is my first attempt at this type of chart and I'm using online examples to help.</p>
  
  <p>Nothing is actually displaying, the paths are getting created but but the data in the paths are all <code>NaN</code>.</p>
  
  <p>I know this is a vague question but can anyome see why this isn't working.</p>
  
  <pre><code>const areaGenerator = d3.area()
    .x((d) =&gt; this.x(d.x))
    .y0(this.height)
    .y1((d) =&gt; this.y(d.y));
  
  const areaGroup = this.chart.append('g')
    .classed('area-group', true)
  
  areaGroup.selectAll('path')
    .data(data)
    .enter()
    .append('path')
    .style('fill', (d, i) =&gt; this.colors[i])
    .attr('d', areaGenerator) 
  </code></pre>