D:\>perl -le "print $1 while 'aaabbcddddaee'=~/((.)\2*)/gs"
aaa
bb
c
dddd
a
ee

##</code><code>##

D:\>perl -le "print for unpack '(a3)*','atgactaatagcagtgg'";
atg
act
aat
agc
agt
gg

##</code><code>##

my @filtered=do { my $i=1; grep $i++ % $N,@unfiltered};