Need help understanding the shuffle cards method

[ProcessingPro]

I don’t understand the //shuffle cards thing.

 //assigning values to each card in the grid
  int[] values = new int[20];
  for (int i=0; i<icons.length; i++) {
   icons[i] = loadImage(filename[i]);
    values[2*i] = i;
    values[2*i+1] = i;
  }

  //shuffle cards
  for (int i=0; i<values.length; i++) {
    int r = int(random(values.length));
    int t = values[i];
    values[i] = values[r];
    values[r] = t;
  }

[GoToLoop]

https://Bost.ocks.org/mike/shuffle/

[kfrajer]

@ProcessingPro

int t = values[i];
values[i] = values[r];
values[r] = t;

This part does a swapping of two items in your array. Your i counter is going through every element in your number container in order, from the first to the last. The r counter is a random item in your list, calculated every time you step in your array.

Kf

[ProcessingPro]

thank you