Hash Manipulation

keys() function

• Returns a list containing all the keys of the hash
   
• Calling keys() on an empty hash returns an empty list
   
• The keys are not in any order: not sorted, not in order added, not nothin'.
   
• Each keys in the list will be unique, because all keys in the hash are unique.

values() function

• Partner of the keys() function
   
• Returns a list containing all the values in the hash
   
• Calling values() on an empty hash returns an empty list
   
• The values are not in any order: not sorted, not in order added, not nothin'.
   
• Values are not necessarily unique, because values in the hash don't have to be.

  my %stats;
  $stats{ "name" } = "Andy Lester";
  $stats{ "age" } = 31;
  
  @keys = keys %stats;
  # @keys is ( "name", "age" ), or maybe ( "age", "name" )
  
  @values = values %stats;
  # @values is ( "Andy Lester", 31 ) or maybe ( 31, "Andy Lester" )

Looping over hashes

• To loop over a hash, get a list of keys, sort it, and loop on it

  my %stats;
  $stats{ "name" } = "Andy Lester";
  $stats{ "age" } = 31;
  my @keys = keys %stats;
  @keys = sort @keys;
  for my $key ( @keys ) {
      print "$key: ", $stats{ $key }, "\n";
      }
  # Prints:
  # age: 31
  # name: Andy Lester

Deleting hash entries

• Use the delete() function to remove a hash entry

  my %stats;
  $stats{ "name" } = "Andy Lester";
  $stats{ "age" } = 31;
  delete $stats{ "name" };
  # %stats now has only one value

• Note that you do NOT want to set the hash element to undef. The hash element will still exist, with a value of undef.