my @refsOfGroups = (); 
my @group;
my $avg;
my $point;

while ( @pointValues) {
   $point = shift @pointValues;
   $avg = average(@group,$point);
   if (   ($avg   - $group[0] > $x_threshold)
        ||($point - $avg      > $x_threshold)
      ) { 
      push @refsOfGroups, [@group];
      @group = ()
   }
   push @group $point; # include the last group
} # while

push @refsOfGroups, [@group];