How to update Apex Chart data via dropdown selection

Question

I'm trying to grasp an understanding of how to change data in Apex Chart from a dropdown selection in Bootstrap vue.

This code pen link shows that the bar chart works fine with a simple dataset of options and series. https://codepen.io/tone373/pen/ZEwYxGL

The below code pen does not work.
https://codepen.io/tone373/pen/JjeYazG

I've added a few functions to the computed property with hopes of changing the data in the chart from dropdown list [A,B]

I believe I'm hung up on the countBy and filter (lodash) methods as well as setting up the data set with aData and bData functions. Am I going about this in the correct way?

if (
    this.selectedChartDisplayBy === "a" ||
    this.selectedChartDisplayBy === "b"
  ) {
    countBy = _.countBy(this.aData, this.selectedChartDisplayBy);
  } else if (this.selectedChartDisplayBy === "b") {
    countBy = _.countBy(this.bData, this.selectedChartDisplayBy);
  }

  let data = [];
  _.map(this.barChartCategories, (cat) => {
    if (!countBy[cat]) {
      data.push(0);
    } else {
      data.push(countBy[cat]);
    }
  });


 barChartCategories() {
  if (this.selectedChartDisplayBy === "a") {
    return _.map(this.aNode, "itemIdentifier").sort();
  } else if (this.selectedChartDisplayBy === "b") {
    return _.map(this.bNode, "itemIdentifier").sort();
  }
},
 aData() {
  var chartData = new Object();
  chartData["aNumbers"] = "[13, 20, 7]";
  return chartData;
},

bData() {
  var chartData = new Object();
  chartData["bNumbers"] = "[6, 10, 17]";
  return chartData;
},
  aNode() {
  return _.filter(this.aData, { type: "a" });
},
bNode() {
  return _.filter(this.bData, { type: "b" });
},