let total = 20;

​

function setup() {

  createCanvas(560,390);

  for (let i = 0; i < total; i++) {

    randomCount[i] = 0;

  }

}

​

function draw() {

  background(220);

  let randomNum = floor(random(total)); //pick a random number

  randomCount[randomNum]++; //increase count

​

  //set rectangle's color

  stroke(63,63,147);

  strokeWeight(2);

  fill(255);

​

  let w = width/randomCount.length; // 560/20 = 28

  //draw a rectangle at location x,y (x*w,height-randomCount[x]) 

  //with a width and height of (w-1,randomCount[x])

  for (let x = 0; x < randomCount.length; x++) {

    rect(x*w,height-randomCount[x],w-1,randomCount[x]);

  }

}