@{$listref} = grep {exists} @{$listref};
maybe you meant:
@{$listref} = map { exists $listref->[$_] ? $listref->[$_] : () } 0 .. $#{$listref} ;
?

update: typo

In reply to Re^4: delete array element from array ref by tinita
in thread delete array element from array ref by llancet

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