I have got a hash that is for all intents and purposes backwards. Basically it is 
my %hash = {
             ball1 => 'red',
             ball2 => 'blue',
             ball3 => 'red',
           };

[download]
and I need the logical equivalent of
%hash = {
           red => "ball1,ball3",
           blue => "ball2",
         }

[download]
I cannot just flop keys for values as I've got a duplicate of red. Any ideas?

In reply to mildly tricky hash question by Anonymous Monk

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