Update data while zooming with D3 and React

Question

I'm using D3 and React to plot a simple line chart with Zoom and Pan behavior. I need to make the data to be relative to the first value on the actual zoom.

For example, if my dataset Y values are [0, 2%, 3% and 4%] and I'm currently viewing the last 3 values, it should plot [0, 1.02%, 2.04%].

I tried to keep a copy of my original dataset and update the viewportDataset on zoom:

_onZoom (zoom) {
  let state = this.state,
      data = state.data,
      viewportData = [],
      filteredData,
      y = state.y,
      x = state.x,
      minDate = d3.min(data, d => d.date),
      maxDate = d3.max(data, d => d.date),
      xZoom, yExtent, yDiff;

  if (x.domain()[0] < minDate) {
    xZoom = zoom.translate()[0] - x(minDate) + x.range()[0];
    zoom.translate([xZoom, 0]);
  }

  else if (x.domain()[1] > maxDate) {
    xZoom = zoom.translate()[0] - x(maxDate) + x.range()[1];
    zoom.translate([xZoom, 0]);
  }

  filteredData = data.filter((d, i) => {
    if ((d.date >= x.domain()[0]) && (d.date <= x.domain()[1])) {
      return [d.daily, d.accumulated, d.dailyRelative];
    }
  });

  let factor = filteredData[0].dailyRelative;

  filteredData.map(d => {
    d.dailyRelative = d.dailyRelative / factor;
    viewportData.push(d);
  });

  y.domain(d3.extent(filteredData, d => d.dailyRelative));

  this.setState({ y, viewportData });
}

React, after setting the new viewportData and Y scale, calls my updateChart chart function:

_updateChart () {
   /* ... */
   let line = chart
    .select('g.data')
    .selectAll('path.line')
    .data([state.viewportData]);

   line.attr('d', d => this._line(d));

   line.enter().append('path.line')
     .attr('d', d => this._line(d));

   line.exit().remove();
}

This approach isn't working. I think I'm not doing the update pattern right. How do I achieve this behavior? I ported my working chart into a pen, heres the code

Answer 1

I ended up updating the data after the zoom event, duh.

Not quite the behavior I was looking for but it's working.

_onZoomend () {
  /* ... */
  chart.select('g.data path.line')
    .transition()
    .attr('d', d => this._line(d, factor));
},