Class: Stacking & Nesting

<!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; }
  </style>
</head>

<body>
  <svg />
  <script>
//     var data = [{
//     	name: 'Sequoia',
//       investments: [
//         {
//         	name: 'Airbnb',
//           amount: 20200, // millions
//           year: 2010,
//           sector: 'consumer'
//         },
//         {
//           name: 'Pinterest',
//           amount: 23874,
//           year: 2008,
//           sector: 'consumer'
//         }
//       ]
//     }, {
      
//     }];
    var data = [{
      name: 'Airbnb',
      amount: 20200, // millions
      year: 2010,
      sector: 'consumer',
      investor: 'Sequoia'
    }, {
      name: 'Pinterest',
      amount: 23874,
      year: 2008,
      sector: 'consumer',
      investor: 'Sequoia'
    }, {
      name: 'Airbnb',
      amount: 20200, // millions
      year: 2010,
      sector: 'consumer',
      investor: 'Benchmark'
    }, {
      name: 'Spotify',
      amount: 239847,
      year: 2091,
      sector: 'consumer',
      investor: 'Benchmark'
    }, {
      name: 'Slack',
      amount: 238947,
      year: 2012,
      sector: 'enterprise',
      investor: 'a16z',
    }, {
      name: 'Slack',
      amount: 238947,
      year: 2012,
      sector: 'enterprise',
      investor: 'Google Ventures',
    }, {
      name: 'Tanium',
      amount: 123987,
      year: 2002,
      sector: 'enterprise',
      investor: 'IVP'
    }, {
      name: 'Lyft',
      amount: 123987,
      year: 2002,
      sector: 'consumer',
      investor: 'a16z'
    }];
    
    // bar chart, x-axis (ordinal) investor
    // y-axis # of unicorns
    // if stacked, sector (consumer vs. enterprise)
    // color by sector
    // hover to see individual unicorns
    
    // 1. group by investor (for x-axis)
    // 2. calculate stack for each sector
    var sectors = data.map(function(d) {return d.sector});
    //console.log(sectors)
    
    data = d3.nest()
    	.key(function(d) {return d.investor})
    	.key(function(d) {return d.sector})
    	.entries(data);
    
    var stack = d3.stack()
    	.keys(['consumer', 'enterprise'])
    	.value(function(investor, key) {
        // if sector key matches key given
        var sector = investor.values.find(function(sector) {return sector.key === key});
        if (!sector) return 0;
        return sector.values.length;
      });
    var series = stack(data);
    console.log(series)
    
    var svg = d3.select('svg')
    	.attr('width', 960)
    	.attr('height', 500);
    
    var sectors = svg.selectAll('g')
    	.data(series, function(d) {return d.key});
    
    sectors.exit().remove();
    
    //sectors is the horizontal group of rectangles
    sectors = sectors.enter().append('g')
    	.classed('sector', true)
    	.merge(sectors);
    
    //rectangles for each investor
    var investor = sectors.selectAll('g') //sectors = <g> parent element
    	.data(function(sector){return sector}, //can pass in function into this .data() b/c data was already appended to the parent
			function(d) {return d.data.key}); //key function keeps track of each rectangle to its original data; the investor.data.key is unique (within the sector), so use that as the ID

investor.exit().remove();  
    
    var enter = investor.enter().append('g');
    enter.append('rect');
    enter.append('text');
    
    investor = enter.merge(investor); //.merge() combines two selections together; investor is update selection!!
    
    investor.select('rect')
    	.attr('x', function(investor, i){return i*25})
    	.attr('y', function(investor){return 500 - investor[1]*100}) //500 = height
    	.attr('width', 20)
    	.attr('height', function(investor){return (investor[1]-investor[0])*100})
    	.attr('fill', '#fff')
    	.attr('stroke', '#000');
    
    investor.select('text')
      .attr('x', function(investor, i){return i*25})
    	.attr('y', function(investor){return 500 - investor[1]*100})
    	.text( function(d){
      	return (d.data.values[0].values[0].name +" "+d.data.values[0].values[0].amount)
    		});

</script>
</body>

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