google "knuth shuffle"

change your colo(u)rs array to an array list.

choose a random number from 0 to list size - 1, get that item from the array list. remember it. delete item from list.
choose a random number from 0 to list size - 1, get that item from the array list. remember it. delete item from list.
choose a random number from 0 to list size - 1, get that item from the array list. remember it. delete item from list.
choose a random number from 0 to list size - 1, get that item from the array list. remember it. delete item from list.
(list should now be empty and you should have 4 things in random order)

Thanks kooogy,

Very interesting indeed. I understand the theory now having looked up the 'knuth shuffle" on wikipedia.

I've also found lots of other similar problems and possible answers on this forum...

Being new to processing however, I think I must be getting confused and changing the examples, (that work perfectly) from strings to colors.

The method I'm trying to replicate creates an array of my colors.... chooses one at random, appends it to a new (and initially empty) array, then deletes it from the original.

My code is still work in progress will post soon once I have tried to figure this out for myself.

Right after lots of head scratching and reading various posts, I have a strategy! But could do with a little more help to get it implemented.

Most of the examples include for loops to automatically process the random selection for large arrays. I would like to also do this eventually but learning the code bit by bit, and as I'm only dealing with 4 different colours, I will code it manually.

I can define the 4 colours and add them to an arrray.... the code I'm using is:

color cr=color(255,0,0);      //defines RED
color cg=color(0,255,0);      //defines GREEN
color cb=color(0,0,255);      //defines BLUE
color cy=color(255,255,0);    //defines YELLOW

color[] colors = {            //adds 4 colours above into array
  cr,cg,cb,cy
};

I can then select a colour at random from the array using:

color c1=(colors[int(random(0,4))]);

with println lines, I know this bit is working.

Next I'm trying to remove the selected colour form the initial array, but the following line:
colors.remove(c1);

Gives the error message:
Cannot invoke remove(int) on the array type int[]

Being new, I'm a little confused. I think I have my data types all mixed up but not sure how to fix it.

All help very much greatly received.

Cool, thanks, getting there bit by bit. I have used to 2 Array Lists where the first one starts off with 4 colours in it.
1 is selected at random, removed and appended to 2nd. This is repeated until all the colours have been moved from first to second array lists. the second array list is in a random order. This is done with the following code:

color cr=color(255,0,0);      //defines RED
color cg=color(0,255,0);      //defines GREEN
color cb=color(0,0,255);      //defines BLUE
color cy=color(255,255,0);    //defines YELLOW
color c1;
color c2;
color c3;
color c4;

void setup() {
  size (420,100);                     //screen size

ArrayList colors=new ArrayList(4);
colors.add(cr);
colors.add(cg);
colors.add(cb);
colors.add(cy);

ArrayList colsel=new ArrayList();

  println (colors);
 
colsel.add(colors.remove(int(random(0,4)))) ;
println (colors);
  println (colsel);
 
  colsel.add(colors.remove(int(random(0,3)))) ;
println (colors);
  println (colsel);
 
  colsel.add(colors.remove(int(random(0,2)))) ;
println (colors);
  println (colsel);
 
  colsel.add(colors.remove(0)) ;
println (colors);
  println (colsel);

My next problem is I'm trying to use:

c1=colsel.get(0);

To start populating the C1, c2, c3 and c4 variables to use as colours.... whatever  I try, (get or remove), the following error message is displayed.

cannot convert form object to int

I suspect this is where the casting comes in but again i'm stuck.... please can someone point me in the directio of how to get this working or at the least explain the casting process.

Many thanks in advance.

Dave

I have only scanned the topic, but I think that you are getting the error because an ArrayList is stored as type Object.
A color is stored weirdly, to put it simply, because it is an int (not an Object), which is why you are getting that error.
To get the color correctly, you need to cast the object to the datatype you are using (in this case a color) using the syntax (color).
In other words,

c1 = (color) colsel.get(0);

By adding this to your code, you get the error 'Cannot cast from Object to int' which is because 'int' is not stored as an Object!

I usually solve this problem by creating a Color class which is an Object and contains a color. This may not be the best method, but I have tried it anyway:
 

Urgh!
The more I think I understand the less I seem to... every little thing I try, works but only to give me a different error.
I think there must be a more simple way to do this.... what about:

Create an Array list
Add my 4 colours to it
Remove one of these at random and assign to col1
Remove the next at random and assign to col2
Remove the next at random and assign to col3
Remove the next, (only one left), at random and assign to col4

Use col1, 2, 3 & 4 to fill the respective blobs on my screen.....

Whatever I try I get into casting issues..... I've tried to find a simple explanation on casting but get bogged down in more complex explanations   / different applications that confuse me.

Sorry to keep bleating on with a simple question but I think I must be missing something. Thanks for any help in advance.

i did say "(you may need to cast the result) " 8)

creating a Color class is a bit of overkill though

you can cast an Object to an Integer and then get the intValue() of that (Integer to int deboxing is done automatically in later versions of java).

something like ((Integer)col2).intValue(); // untested

(alternatively, depending on java and processing version) you can define your ArrayList as containing Integers:
ArrayList<Integer> list new = ArrayList<Integer>();
and then you won't need to cast the result, but may need to convert from Integer to int to color)

it's fiddly.