If performance is not your utmost concern, I would use two grep statements to filter out lines with and without Y at the end. It would the look like this:

use strict;
use warnings;

my @result  = <DATA>;
my @streams = map /^(\S+)/, grep /\sY$/, @result;
my @spaces  = map /^(\S+)/, grep !/\sY$/, @result;
print "streams: @streams\n";
print "spaces: @spaces\n";

__DATA__
ws.abc.dsfsfsfwerfrwef std 13232
ws.dfsdferferfregregrgr std 99868 Y
ws.abc.asddwefewfewfewf std 45345
fwfrwfrefergegregerefds std 36754 Y
ws.abc.fferfergregrfreg std 45435
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And if you are concerned about the three fields versus four fields issue, you could modify the condition in the grep statement accordingly.