ikegami has already posted an excellent reply, showing exactly how to do it with while. That is probably the best way to solve this particular problem, but I thought I would show you how to use map to filter out elements, for your future reference:

my @array = qw(foo bar baz qux);

my @newarray = map  { my $foo = $_;
                      $foo =~ s/./\u$&/; # useless example
                      $foo =~ /Ba/
                        ? $foo
                        : () }
               grep { /a/ }
               @array;
[download]

The key here is to return an empty list when the condition fails. It's neat that we can do this with map, but it's usually better to use another grep:

my @array = qw(foo bar baz qux);

my @newarray = grep { /Ba/ }
               map  { my $foo = $_;
                      $foo =~ s/./\u$&/; # useless example
                      $foo }
               grep { /a/ }
               @array;
[download]

HTH