Category vs. Default bar chart

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin: 0; position: fixed; top: 0; right: 0; bottom: 0; left: 0; }
    svg { width: 100%; height: 100%; }
  </style>
</head>

<body>
  <svg></svg>
  <script>
    // options
    var margin = {"top": 20, "right": 10, "bottom": 40, "left": 40 }
    var width = 500;
    var height = 500;
    var rectWidth = 60;
    var topPadding = 1.05;
    
    // data
    var data = [[0, 100],
               	[0, 150],
               	[0, 50]
               ];
    
    var colors = ["white", "teal"]
    
    // ticks
    var x_ticks = ["Bachelor's", "Master's", "PhD"];
    
    // calculate column totals
    let colTotals = function(data) {
      var cols = [];
      for (var i = 0; i < data.length; i++){
        var col = data[i].reduce(function(sum, value){
          return (sum + value)}, 0);
        	cols.push(col);
      }
      return cols;
    }  
      
    // calculate yMax
    let dataMax = function(data) {
      var colHeights = colTotals(data);
      return d3.max(colHeights) * topPadding;
    }
    
    // scales
    var xAxisScale = d3.scaleBand()
    	.domain(x_ticks)
    	.range([margin.left, width - margin.right]);
    var xDataScale = d3.scaleBand()
    	.domain([0, 1, 2])
    	.range([margin.left, width - margin.right])
    	.paddingInner(0.2)
    	.paddingOuter(0.2)
    var yMax = dataMax(data);
    var yAxisScale = d3.scaleLinear()
    	.domain([0, yMax])
    	.range([height - margin.bottom, margin.top]);
     
    // svg element
    var svg = d3.select('svg');
	
    
    // create bars array
    let flatten = function(data, colors) {   
      var bars = [];
      var barTotals = colTotals(data);
      for (var i = 0; i < data.length; i++) {
        var yStart = 0;
        for (var j = 0; j < data[i].length; j++) {     
          if (j != 0) {
            yStart += data[i][j-1];
          }
          var bar = {
            "x" : i,
            "y" : yStart+data[i][j],
            "yStart": yStart,
            "height" : data[i][j],
            "color" : colors[j],
            "empty" : false
          };
          bars.push(bar);  
        }
      } 
      return {"bars": bars, "barTotals": barTotals};
    }
    
    // draw bars
    var rectData = flatten(data, colors); 
    var bars = rectData.bars;
    var barTotals = rectData.barTotals;
   	svg.selectAll('rect')
      .data(bars)
      .enter().append('rect')
      .attr('x', function(d, i){
      	return xDataScale(bars[i].x)}) 
      .attr('y', function(d, i){
      	return yAxisScale(bars[i].y)})
      .attr('width', xDataScale.bandwidth)
      .attr('height', function(d, i){
      	return yAxisScale(bars[i].yStart) - yAxisScale(bars[i].y)}) 
      .attr('fill',function (d, i){
      	if (bars[i].empty){
          return "white";
        }else{
          return bars[i].color;
        }})
      .attr('stroke', 'white')
         
    // axes
    var xAxis = d3.axisBottom()
    	.scale(xAxisScale)
    var yAxis = d3.axisLeft()
    	.scale(yAxisScale)
    	.ticks(5)
    
   // draw axes
   svg.append('g')
     .attr('transform', 'translate(' + [0, height - margin.bottom] + ')')
     .call(xAxis);
   svg.append('g')
     .attr('transform', 'translate(' + [margin.left, 0] + ')')
     .call(yAxis); 
  </script>
</body>

https://d3js.org/d3.v4.min.js