Tie::IxHash

Tie::IxHash(3pm)      User Contributed Perl Documentation     Tie::IxHash(3pm)



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 recom-
       mended 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 follow-
       ing 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 avail-
               able for operating on key-value pairs in the IxHash. The behav-
               ior 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 corre-
               sponding 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 con-
               vert 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 corre-
               sponding 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 corre-
               sponding 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 sub-
               stitutes the value at index with the supplied value. If an ele-
               ment 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 val-
               ues.

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.

       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 AT 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 1.21    20 Nov 1997

SEE ALSO
       perl(1)



perl v5.8.8                       1997-11-20                  Tie::IxHash(3pm)