the

grep{$_} .......
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also removes "" and 0 from the list. Should probably be

grep{defined $_} .....
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Also - why use

@array -1
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when you could use

$#array
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I like the approach.... Perhaps

map{[
   grep {defined}
   @array[$_*$len..$_*$len+$len-1]
   ]} 0..$#array/$len
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Is a little cleaner?