Why not iterate over the data set, a line at a time, using a regex to capture all required occurrences...

$ perl -e 'my $t = "1,2,3,4,1,1,1,3,5,1,1,1,1"; my @s = $t =~ /(1,1),?/g; my @f = $t =~ /(1,2),?/g; die sprintf "%d success(es), %d failure(s)", scalar @s, scalar @f' returns 3 success(es), 1 failure(s) at -e line 1 ... as expected - with no warnings :-)