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<HTML><HEAD><TITLE>Recipe 5.6. Retrieving from a Hash in Insertion Order (Perl Cookbook)</TITLE><METANAME="DC.title"CONTENT="Perl Cookbook"><METANAME="DC.creator"CONTENT="Tom Christiansen & Nathan Torkington"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1999-07-02T01:32:37Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-243-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch05_01.htm"TITLE="5. Hashes"><LINKREL="prev"HREF="ch05_06.htm"TITLE="5.5. Printing a Hash"><LINKREL="next"HREF="ch05_08.htm"TITLE="5.7. Hashes with Multiple Values Per Key"></HEAD><BODYBGCOLOR="#FFFFFF"><img alt="Book Home" border="0" src="gifs/smbanner.gif" usemap="#banner-map" /><map name="banner-map"><area shape="rect" coords="1,-2,616,66" href="index.htm" alt="Perl Cookbook"><area shape="rect" coords="629,-11,726,25" href="jobjects/fsearch.htm" alt="Search this book" /></map><div class="navbar"><p><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch05_06.htm"TITLE="5.5. Printing a Hash"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 5.5. Printing a Hash"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1"><ACLASS="chapter"REL="up"HREF="ch05_01.htm"TITLE="5. Hashes"></A></FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch05_08.htm"TITLE="5.7. Hashes with Multiple Values Per Key"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 5.7. Hashes with Multiple Values Per Key"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch05-11275">5.6. Retrieving from a Hash in Insertion Order</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-592">Problem</A></H3><PCLASS="para"><ACLASS="indexterm"NAME="ch05-idx-1000006466-0"></A><ACLASS="indexterm"NAME="ch05-idx-1000006466-1"></A>The <CODECLASS="literal">keys</CODE> and <CODECLASS="literal">each</CODE> functions give you the hash elements in a strange order, and you want them in the order in which you inserted them.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-598">Solution</A></H3><PCLASS="para">Use the <ACLASS="indexterm"NAME="ch05-idx-1000006467-0"></A>Tie::IxHash module.</P><PRECLASS="programlisting">use Tie::IxHash;tie %HASH, "Tie::IxHash";# manipulate %HASH@keys = keys %HASH; # @keys is in insertion order</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-612">Discussion</A></H3><PCLASS="para">Tie::IxHash makes <CODECLASS="literal">keys</CODE>, <CODECLASS="literal">each</CODE>, and <CODECLASS="literal">values</CODE> return the hash elements in the order they were added. This often removes the need to preprocess the hash keys with a complex <CODECLASS="literal">sort</CODE> comparison or maintain a distinct array containing the keys in the order they were inserted into the hash.</P><PCLASS="para">Tie::IxHash also provides an object-oriented interface to <CODECLASS="literal">splice</CODE>, <CODECLASS="literal">push</CODE><ACLASS="indexterm"NAME="ch05-idx-1000006469-0"></A> , <CODECLASS="literal">pop</CODE>, <CODECLASS="literal">shift</CODE>, <CODECLASS="literal">unshift</CODE>, <CODECLASS="literal">keys</CODE>, <CODECLASS="literal">values</CODE>, and <CODECLASS="literal">delete</CODE>, among others. <ACLASS="indexterm"NAME="ch05-idx-1000006468-0"></A><ACLASS="indexterm"NAME="ch05-idx-1000006468-1"></A><ACLASS="indexterm"NAME="ch05-idx-1000006468-2"></A><ACLASS="indexterm"NAME="ch05-idx-1000006468-3"></A><ACLASS="indexterm"NAME="ch05-idx-1000006468-4"></A><ACLASS="indexterm"NAME="ch05-idx-1000006468-5"></A><ACLASS="indexterm"NAME="ch05-idx-1000006468-6"></A></P><PCLASS="para">Here's an example, showing both <CODECLASS="literal">keys</CODE> and <CODECLASS="literal">each</CODE>:</P><PRECLASS="programlisting"># initializeuse Tie::IxHash;tie %food_color, "Tie::IxHash";$food_color{Banana} = "Yellow";$food_color{Apple} = "Green";$food_color{Lemon} = "Yellow";print "In insertion order, the foods are:\n";foreach $food (keys %food_color) { print " $food\n";}print "Still in insertion order, the foods' colors are:\n";while (( $food, $color ) = each %food_color ) { print "$food is colored $color.\n";}<CODECLASS="userinput"><B><CODECLASS="replaceable"><I>In insertion order, the foods are:</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I> Banana</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I> Apple</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I> Lemon</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I>Still in insertion order, the foods' colors are:</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I>Banana is colored Yellow.</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I>Apple is colored Green.</I></CODE></B></CODE><CODECLASS="userinput"><B><CODECLASS="replaceable"><I>Lemon is colored Yellow.</I></CODE></B></CODE></PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-674">See Also</A></H3><PCLASS="para">The documentation for the CPAN module Tie::IxHash; <ACLASS="xref"HREF="ch13_16.htm"TITLE="Creating Magic Variables with tie">Recipe 13.15</A></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="684"TITLE="footer"><TABLEWIDTH="684"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch05_06.htm"TITLE="5.5. 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