You could use a do block to avoid having the -d directory test twice.

$ ls -F
fred  testFBF*  xxx/  yyy/
$ perl -Mstrict -Mwarnings -E '
my @dirs = qw{ fred testFBF xxx yyy };
@dirs    = map {
   -d $_
   ? $_
   : do { warn qq{Not a directory: $_\n}; () }
   } @dirs;
say qq{Directories: @dirs};'
Not a directory: fred
Not a directory: testFBF
Directories: xxx yyy
$
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I hope this is of interest.