Mergesort II: commented

An improved animation of mergesort. As the name suggests, the algorithm merges sorted arrays, starting with arrays of length 1 and doubling at each step. The two subarrays currently being merged are shown in black.

forked from mbostock's block: Mergesort II

forked from anonymous's block: Mergesort II: commented

<!DOCTYPE html>
<meta charset="utf-8">
<style>

.line {
  stroke: #000;
  stroke-width: 1.5px;
  stroke-linecap: round;
}

.line--inactive {
  stroke: #ddd;
  stroke-width: 1px;
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

// 1: data is array of numbers from 0 to 199, randomly ordered
var n = 200,
    array = d3.shuffle(d3.range(n)),
    actions = mergesort(array.slice()).reverse();

var margin = {top: 180, right: 40, bottom: 180, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

// y translates ...
var y = d3.scale.ordinal()
    .domain([1, 0])
    .rangeRoundBands([height, 0], .3);

var x = d3.scale.ordinal()
    .domain(d3.range(n))
    .rangePoints([0, width]);

var a = d3.scale.linear()
    .domain([0, n - 1])
    .range([-45, 45]);

var svg = d3.select("body").append("svg")
    .attr("width", width + margin.left + margin.right)
    .attr("height", height + margin.top + margin.bottom)
  .append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

var line = svg.append("g")
    .attr("class", "line")
  .selectAll("line")
    .data(array.map(function(v, i) {
      return {
        // 2. v is the value
        value: v,
        // index is the position
        index: i,
        // set array to 0, will alternate between 0 and 1
        array: 0
      };
    }))
	// 3: each datapoint is represented with a line
  .enter().append("line")
		// 4: each line has a transformation applied and is given a "y2" value
		// y1, x1, and x2 are set implicitely to 0
		// what is the transformation? 
    .attr("transform", transform)
    .attr("y2", -y.rangeBand());

var line0 = line[0],
    line1 = new Array(n);

// 5: transformation is a translation horiztonally, vertically, and a rotation
function transform(d) {
  // what is the x, y, and a functions?
  return "translate(" + x(d.index) + "," + y(d.array) + ")rotate(" + a(d.value) + ")";
}

function mergesort(array) {
  var actions = [],
      n = array.length,
      array0 = array,
      array1 = new Array(n);

for (var m = 1; m < n; m <<= 1) {
    for (var i = 0; i < n; i += (m << 1)) {
      merge(i, Math.min(i + m, n), Math.min(i + (m << 1), n));
    }
    actions.push({type: "swap"});
    array = array0, array0 = array1, array1 = array;
  }

return actions;
}

</script>

https://d3js.org/d3.v3.min.js