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foreach my $id (
    map { $_->[1] }
...
{
    printf "$id\t$students{$id}\n";
}

4873    Tom     2.9
236     Fred    3.2
1522    Susan   4.0

    # Create a list of student IDs by taking the sorted
    # list of anonymous arrays and returning the second
...
    # the value of $students{$_} on the tab, and the second
    # element is the student ID.
    map { [ (split( "\t", $students{$_} ))[1], $_ ] } keys %students )