# phpman > perldoc > Tie::IxHash

## NAME
    [Tie::IxHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3AIxHash/markdown) - ordered associative arrays for Perl

## SYNOPSIS
        # simple usage
        use [Tie::IxHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3AIxHash/markdown);
        tie HASHVARIABLE, '[Tie::IxHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3AIxHash/markdown)' [, LIST];

        # OO interface with more powerful features
        use [Tie::IxHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3AIxHash/markdown);
        TIEOBJECT = [Tie::IxHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3AIxHash/markdown)->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)](https://www.chedong.com/phpMan.php/man/perlfunc/1/markdown) 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](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3AIxHash/markdown);

        # simple interface
        $t = tie(%myhash, '[Tie::IxHash](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3AIxHash/markdown)', '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](https://www.chedong.com/phpMan.php/perldoc/Tie%3A%3AIxHash/markdown)->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