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<HTML><HEAD><TITLE>Recipe 5.14. Finding the Most Common Anything (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="1999-07-02T01:32:56Z"><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_14.htm"TITLE="5.13. Presizing a Hash"><LINKREL="next"HREF="ch05_16.htm"TITLE="5.15. Representing Relationships Between Data"></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_14.htm"TITLE="5.13. Presizing a Hash"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 5.13. Presizing 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_16.htm"TITLE="5.15. Representing Relationships Between Data"><IMGSRC="../gifs/txtnexta.gif"ALT="Next: 5.15. Representing Relationships Between Data"BORDER="0"></A></TD></TR></TABLE></DIV><DIVCLASS="sect1"><H2CLASS="sect1"><ACLASS="title"NAME="ch05-chap05_finding_1">5.14. Finding the Most Common Anything</A></H2><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-1270">Problem<ACLASS="indexterm"NAME="ch05-idx-1000006515-0"></A><ACLASS="indexterm"NAME="ch05-idx-1000006515-1"></A></A></H3><PCLASS="para">You have an aggregate data structure, such as an array or a hash. You want to know how often each element in the array (or key or value in the hash) occurs. For instance, if your array contains web server transactions, you might want to find the most commonly requested file. If your hash maps usernames to number of logins, you want to find the most common number of logins.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-1276">Solution</A></H3><PCLASS="para">Use a hash to count how many times each element, key, or value appears:</P><PRECLASS="programlisting">%count = ();foreach $element (@ARRAY) { $count{$element}++;}</PRE></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-1290">Discussion</A></H3><PCLASS="para">Any time you want to count how often different things appear, you should probably be using a hash. The <CODECLASS="literal">foreach</CODE> adds one to <CODECLASS="literal">$count{$element}</CODE> for every occurrence of <CODECLASS="literal">$element</CODE>.</P></DIV><DIVCLASS="sect2"><H3CLASS="sect2"><ACLASS="title"NAME="ch05-pgfId-1296">See Also</A></H3><PCLASS="para"><ACLASS="xref"HREF="ch04_07.htm"TITLE="Extracting Unique Elements from a List">Recipe 4.6</A>; <ACLASS="xref"HREF="ch04_08.htm"TITLE="Finding Elements in One Array but Not Another">Recipe 4.7</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_14.htm"TITLE="5.13. Presizing a Hash"><IMGSRC="../gifs/txtpreva.gif"ALT="Previous: 5.13. 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