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<HTML><HEAD><TITLE>Recipe 5.9. Sorting a Hash (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="1999-07-02T01:32:46Z"><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_09.htm"TITLE="5.8. Inverting a Hash"><LINKREL="next"HREF="ch05_11.htm"TITLE="5.10. Merging Hashes"></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_09.htm"TITLE="5.8. Inverting a Hash"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 5.8. Inverting 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_11.htm"TITLE="5.10. Merging Hashes"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 5.10. Merging Hashes"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch05-29376">5.9. Sorting a Hash</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-904">Problem<ACLASS="indexterm"NAME="ch05-idx-1000006489-0"></A><ACLASS="indexterm"NAME="ch05-idx-1000006489-1"></A></A></H3><PCLASS="para">You need to work with the elements of a hash in a particular order.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-1000006885">Solution</A></H3><PCLASS="para">Use <CODECLASS="literal">keys</CODE><ACLASS="indexterm"NAME="ch05-idx-1000006886-0"></A><ACLASS="indexterm"NAME="ch05-idx-1000006886-1"></A> to get a list of the keys, then <CODECLASS="literal">sort</CODE> them based on the ordering you want:</P><PRECLASS="programlisting"># %HASH is the hash to sort@keys = sort { criterion() } (keys %hash);foreach $key (@keys) { $value = $hash{$key}; # do something with $key, $value}</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-928">Discussion</A></H3><PCLASS="para">Even though you can't directly maintain a hash in a specific order (unless you use the Tie::IxHash module mentioned in <ACLASS="xref"HREF="ch05_07.htm"TITLE="Retrieving from a Hash in Insertion Order">Recipe 5.6</A>), you can access its entries in any order.</P><PCLASS="para">This technique offers many variations on the same basic mechanism: You extract the keys, reorder them using the <CODECLASS="literal">sort</CODE> function, and then process the entries in the new order. All the sorting tricks shown in <ACLASS="xref"HREF="ch04_01.htm"TITLE="Arrays">Chapter 4, <CITECLASS="chapter">Arrays</CITE></A>, can be used here. Let's look at some applications.</P><PCLASS="para">The following code simply uses <CODECLASS="literal">sort</CODE> to order the keys alphabetically:</P><PRECLASS="programlisting">foreach $food (sort keys %food_color) { print "$food is $food_color{$food}.\n";}</PRE><PCLASS="para">This sorts the keys by their associated values:</P><PRECLASS="programlisting">foreach $food (sort { $food_color{$a} cmp $food_color{$b} } keys %food_color) { print "$food is $food_color{$food}.\n";}</PRE><PCLASS="para">This sorts by length of the values:</P><PRECLASS="programlisting">@foods = sort { length($food_color{$a}) <=> length($food_color{$b}) } keys %food_color;foreach $food (@foods) { print "$food is $food_color{$food}.\n";}</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-962">See Also</A></H3><PCLASS="para">The <CODECLASS="literal">sort</CODE> and <CODECLASS="literal">keys</CODE> functions in <ICLASS="filename">perlfunc </I>(1) and in <ACLASS="olink"HREF="../prog/ch03_01.htm">Chapter 3</A> of <ACLASS="citetitle"HREF="../prog/index.htm"TITLE="Programming Perl"><CITECLASS="citetitle">Programming Perl</CITE></A>; <ACLASS="xref"HREF="ch05_07.htm"TITLE="Retrieving from a Hash in Insertion Order">Recipe 5.6</A>; we discuss sorting lists in <ACLASS="xref"HREF="ch04_16.htm"TITLE="Sorting a List by Computable Field">Recipe 4.15</A> <ACLASS="indexterm"NAME="ch05-idx-1000006492-0"></A><ACLASS="indexterm"NAME="ch05-idx-1000006492-1"></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_09.htm"TITLE="5.8. Inverting a Hash"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 5.8. Inverting a Hash"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><ACLASS="book"HREF="index.htm"TITLE="Perl Cookbook"><IMGSRC="../gifs/txthome.gif"ALT="Perl Cookbook"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228"><ACLASS="sect1"HREF="ch05_11.htm"TITLE="5.10. Merging Hashes"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 5.10. Merging Hashes"BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="228">5.8. Inverting a Hash</TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="228"><ACLASS="index"HREF="index/index.htm"TITLE="Book Index"><IMGSRC="../gifs/index.gif"ALT="Book Index"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="228">5.10. 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