NAME

       Tie::IxHash - ordered associative arrays for Perl

SYNOPSIS

           # simple usage
           use Tie::IxHash;
           tie HASHVARIABLE, 'Tie::IxHash' [, LIST];

           # OO interface with more powerful features
           use Tie::IxHash;
           TIEOBJECT = Tie::IxHash->new( [LIST] );
           TIEOBJECT->Splice( OFFSET [, LENGTH [, LIST]] );
           TIEOBJECT->Push( LIST );
           TIEOBJECT->Pop;
           TIEOBJECT->Shift;
           TIEOBJECT->Unshift( LIST );
           TIEOBJECT->Keys( [LIST] );
           TIEOBJECT->Values( [LIST] );
           TIEOBJECT->Indices( LIST );
           TIEOBJECT->Delete( [LIST] );
           TIEOBJECT->Replace( OFFSET, VALUE, [KEY] );
           TIEOBJECT->Reorder( LIST );
           TIEOBJECT->SortByKey;
           TIEOBJECT->SortByValue;
           TIEOBJECT->Length;

DESCRIPTION

       This Perl module implements Perl hashes that preserve the order in which the hash elements
       were added.  The order is not affected when values corresponding to existing keys in the
       IxHash are changed.  The elements can also be set to any arbitrary supplied order.  The
       familiar perl array operations can also be performed on the IxHash.

   Standard "TIEHASH" Interface
       The standard "TIEHASH" mechanism is available. This interface is recommended for simple
       uses, since the usage is exactly the same as regular Perl hashes after the "tie" is
       declared.

   Object Interface
       This module also provides an extended object-oriented interface that can be used for more
       powerful operations with the IxHash.  The following methods are available:

       FETCH, STORE, DELETE, EXISTS
               These standard "TIEHASH" methods mandated by Perl can be used directly.  See the
               "tie" entry in perlfunc(1) for details.

       Push, Pop, Shift, Unshift, Splice
               These additional methods resembling Perl functions are available for operating on
               key-value pairs in the IxHash. The behavior is the same as the corresponding perl
               functions, except when a supplied hash key already exists in the hash. In that
               case, the existing value is updated but its order is not affected.  To
               unconditionally alter the order of a supplied key-value pair, first "DELETE" the
               IxHash element.

       Keys    Returns an array of IxHash element keys corresponding to the list of supplied
               indices.  Returns an array of all the keys if called without arguments.  Note the
               return value is mostly only useful when used in a list context (since perl will
               convert it to the number of elements in the array when used in a scalar context,
               and that may not be very useful).

               If a single argument is given, returns the single key corresponding to the index.
               This is usable in either scalar or list context.

       Values  Returns an array of IxHash element values corresponding to the list of supplied
               indices.  Returns an array of all the values if called without arguments.  Note
               the return value is mostly only useful when used in a list context (since perl
               will convert it to the number of elements in the array when used in a scalar
               context, and that may not be very useful).

               If a single argument is given, returns the single value corresponding to the
               index.  This is usable in either scalar or list context.

       Indices Returns an array of indices corresponding to the supplied list of keys.  Note the
               return value is mostly only useful when used in a list context (since perl will
               convert it to the number of elements in the array when used in a scalar context,
               and that may not be very useful).

               If a single argument is given, returns the single index corresponding to the key.
               This is usable in either scalar or list context.

       Delete  Removes elements with the supplied keys from the IxHash.

       Replace Substitutes the IxHash element at the specified index with the supplied value-key
               pair.  If a key is not supplied, simply substitutes the value at index with the
               supplied value. If an element with the supplied key already exists, it will be
               removed from the IxHash first.

       Reorder This method can be used to manipulate the internal order of the IxHash elements by
               supplying a list of keys in the desired order.  Note however, that any IxHash
               elements whose keys are not in the list will be removed from the IxHash.

       Length  Returns the number of IxHash elements.

       SortByKey
               Reorders the IxHash elements by textual comparison of the keys.

       SortByValue
               Reorders the IxHash elements by textual comparison of the values.

       Clear   Resets the IxHash to its pristine state: with no elements at all.

EXAMPLE

           use Tie::IxHash;

           # simple interface
           $t = tie(%myhash, 'Tie::IxHash', 'a' => 1, 'b' => 2);
           %myhash = (first => 1, second => 2, third => 3);
           $myhash{fourth} = 4;
           @keys = keys %myhash;
           @values = values %myhash;
           print("y") if exists $myhash{third};

           # OO interface
           $t = Tie::IxHash->new(first => 1, second => 2, third => 3);
           $t->Push(fourth => 4); # same as $myhash{'fourth'} = 4;
           ($k, $v) = $t->Pop;    # $k is 'fourth', $v is 4
           $t->Unshift(neg => -1, zeroth => 0);
           ($k, $v) = $t->Shift;  # $k is 'neg', $v is -1
           @oneandtwo = $t->Splice(1, 2, foo => 100, bar => 101);

           @keys = $t->Keys;
           @values = $t->Values;
           @indices = $t->Indices('foo', 'zeroth');
           @itemkeys = $t->Keys(@indices);
           @itemvals = $t->Values(@indices);
           $t->Replace(2, 0.3, 'other');
           $t->Delete('second', 'zeroth');
           $len = $t->Length;     # number of key-value pairs

           $t->Reorder(reverse @keys);
           $t->SortByKey;
           $t->SortByValue;

BUGS

       You cannot specify a negative length to "Splice". Negative indexes are OK, though.

NOTE

       Indexing always begins at 0 (despite the current $[ setting) for all the functions.

TODO

       Addition of elements with keys that already exist to the end of the IxHash must be
       controlled by a switch.

       Provide "TIEARRAY" interface when it stabilizes in Perl.

       Rewrite using XSUBs for efficiency.

AUTHOR

       Gurusamy Sarathy        gsar@umich.edu

       Copyright (c) 1995 Gurusamy Sarathy. All rights reserved.  This program is free software;
       you can redistribute it and/or modify it under the same terms as Perl itself.

VERSION

       Version 1.23

SEE ALSO

       perl(1)