use strict;
use warnings;

my %Names = (A => 1,  B => 1, C => 1);
my %FullRecord = (A_1 => 1, D_4 => 1, C_3 => 1, F_6 => 1, B_2 => 1,);
my @DesiredRecord = ();

foreach my $el (keys(%FullRecord)) {
  my @SplitArray=split(/\_/,$el);
  unshift(@DesiredRecord, $el) if exists $Names{$SplitArray[0]};
}
print "@DesiredRecord";
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