Javascript merge sort visualisation

Question

I have managed to get a merge sort working in p5.js to sort different length lines but can not figure out how to actually show them being sorted. I.e show them unsorted and then

Answer 1

This answer uses a non-recursive merge sort that keeps a history of the stages of the sort. The entire sort is performed before draw and then draw steps through all the stages so that we can see how the algorithm moves the lines to achieve the sort. The code is adapted from Mike Bostock's Visualizing Algorithms.

https://bost.ocks.org/mike/algorithms/ https://bl.ocks.org/mbostock/1b5450d525babd28425f

var values = [];
var numLines = 500;
var sortHist = [];
function setup() {
  createCanvas(900, 600);
  colorMode(HSB, height);
  for (i = 0; i < numLines; i++) {
    values[i] =random(height);
  }
  sortHist = mergeSort(values);
  frameRate(1);
}
  
var historyIndex = 0;
function draw() {
  background(51);
  for (i = 0; i < sortHist[historyIndex].length; i++) {
    let col = color(sortHist[historyIndex][i], height, height);
    stroke(col);
    fill(col);
    var location = map(i, 0, sortHist[historyIndex].length, 0, width);
    rect(location, height - sortHist[historyIndex][i], width/numLines, height);
  } 
  historyIndex++;
  if (historyIndex > sortHist.length -1){
    noLoop();
  }
}

function mergeSort(array) {
  var arrays = [array.slice()],
  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));
    }
    arrays.push(array1.slice());
    array = array0, array0 = array1, array1 = array;
  }

function merge(left, right, end) {
  for (var i0 = left, i1 = right, j = left; j < end; ++j) {
    array1[j] = array0[i0 < right && (i1 >= end || array0[i0] <=    array0[i1]) ? i0++ : i1++];
   }
 }
 return arrays;
}