Shell Programming and Scripting

awk '
$2==p{c++;next}
p && c>1{ print p, c}
{p=$2;c=1}
END{if(c>1)print p, c}' file

$2 == p { c++; next; }
p != "" && c { print p, c; }
{ p = $2 ; c = 1; n[p]++; }
END {
  if (p != "") print p, c;
  print "==============";
  for (p in n) print p, n[p];
}

while(<DATA>){
  my @tmp = split;
  if($.==1){
   $pre=$tmp[1];
   $cnt=1;
   next;
  }
  else{
   if($tmp[1] eq $pre){
     $cnt++;
   }
   else{
    $hash{$pre}->{$cnt}=1;
    $cnt=1;
    $pre=$tmp[1];
  }
 }
}
$hash{$pre}->{$cnt}=1;
foreach my $key (keys %hash){
  my %tmp = %{$hash{$key}};
  foreach my $k (keys %tmp){
   print $key,":", $k,"\n" if $k>1;
  }
}
__DATA__
Student1 arts
Student2 science
Student3 arts
Student4 science
Student5 science
Student6 science
Student7 science
Student8 science
Student9 science
Student10 science
Student11 science
Student12 arts
Student13 arts
Student14 arts
Student15 arts
Student16 science
Student17 science
Student18 science
Student19 science
Student20 science

use strict;
use warnings;

$\ = "\n";
$, = ':';

my $p = '';
my $n = 0;
my %N = ();

while (<>) {
    chomp;
    my ($s, $c) = split;

    if ($c ne $p) {
        print $p, $n if 0 < $n;

        $N{$c}++;
        $p = $c;
        $n = 0;
    }

    $n++;
}

print $p, $n if 0 < $n;
print '=' x 10;
while (my ($c, $n) = each %N) { print $c, $n; }

uniq -f1 -c