# { student name => grade }
my %grades = ( "Bob" => 3.2, "Alice" => 3.9 );

# { node name => [ child node ] }
my %graph = ( A => [ "B", "C" ], B => [ "D" ] );

# { student name => { "age" => age, "grade" => GPA } }
my %students = ( "Bob" => { age => 34, grade => 3.2 } );

# { name => <age, children, dirty flag> }
# where children : { child name => 1 }
my %table = ...;
print "Bob is $table{Bob}->[0] years old.\n";
print "His children are ", join(" ", keys %{ $table{Bob}[1] }), "\n";
print "Is Guido his child? ";
print ($table{Bob}[1]{Guido} ? "yes" : "no"), "\n";

# My version of your example
#
# Returns: [ stat chunk ]
#  where stat chunk :
#    { "originals" => { id => value },
#      "changes" => { id => value },
#      "means" => <mean of originals, mean of changes>,
#      "variances" => <variance of originals, variance of changes>
#    }
#
# or you could give a symbolic name to the { id => value } things.