Re: Randomize order of an array?

Posted by dscho on Feb 27, 2009; 10:10pm
URL: http://imagej.273.s1.nabble.com/Randomize-order-of-an-array-tp3693530p3693535.html

Hi,

On Fri, 27 Feb 2009, Mike Myerburg wrote:

> I use a modified version of the BatchProcessFolders Macro to analyze all
> the images in a folder.  In order to be as objective as possible, I
> would like to randomize the order that the images are processed (I have
> already blanked out the filename, so I cant cheat that way).  Here is a
> snippet of the macro that call sends each file to processFile-
>
>  function processFiles(dir) {
>       list = getFileList(dir);
>       for (i=0; i<list.length; i++) {
>           if (endsWith(list[i], "/"))
>               processFiles(""+dir+list[i]);
>           else {
>              showProgress(n++, count);
>              path = dir+list[i];
>              processFile(path);
>           }
>       }
>   }
>
> The array list then would contain the ordered list of files.  Is there a
> way to randomize the order of these file in the array using the macro
> language?

Maybe you want something like this (totally untested):

function randomize(array) {
        for (i = 0; i < array.length - 1; i++) {
                j = i + floor(random() * (array.length - i));
                if (i != j) {
                        swap = array[j];
                        array[j] = array[i];
                        array[i] = swap;
                }
        }
}

The idea is to iterate over all indices (except the last one), pick a
random index greater or equal to that index, and swap the respective list
items.  (You might need to fix the code to implement that idea; as I said,
I did not test.)

You would call the function directly after calling getFileList():

        list = randomize(list);

However, I see that you may have subdirectories; you will have to build a
complete list of all files before randomizing in order to get an unbiased
result.

Ciao,
Dscho