I just chose to write it as a list operator so that you could say

@result = group 1,2,2,2,3,3,4,4,4,4,5,5,6,6;
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instead of doing it all with "scalar" arrays:

@result := group [1,2,2,2,3,3,4,4,4,4,5,5,6,6];
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But either approach is fine.