In your code above, you are creating @a & @b as arrays of references to (one element) arrays. Perhaps what you intend is something like: 
my @a = map { ${ $_ }[0] ] @S;

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TJD

In reply to Re^3: How to save first two columns of an array into another array by Anonymous Monk
in thread How to save first two columns of an array into another array by zing

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