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<html><head><title>Arrays of Hashes (Programming Perl)</title><!-- STYLESHEET --><link rel="stylesheet" type="text/css" href="../style/style1.css"><!-- METADATA --><!--Dublin Core Metadata--><meta name="DC.Creator" content=""><meta name="DC.Date" content=""><meta name="DC.Format" content="text/xml" scheme="MIME"><meta name="DC.Generator" content="XSLT stylesheet, xt by James Clark"><meta name="DC.Identifier" content=""><meta name="DC.Language" content="en-US"><meta name="DC.Publisher" content="O'Reilly & Associates, Inc."><meta name="DC.Source" content="" scheme="ISBN"><meta name="DC.Subject.Keyword" content=""><meta name="DC.Title" content="Arrays of Hashes"><meta name="DC.Type" content="Text.Monograph"></head><body><!-- START OF BODY --><!-- TOP BANNER --><img src="gifs/smbanner.gif" usemap="#banner-map" border="0" alt="Book Home"><map name="banner-map"><AREA SHAPE="RECT" COORDS="0,0,466,71" HREF="index.htm" ALT="Programming Perl"><AREA SHAPE="RECT" COORDS="467,0,514,18" HREF="jobjects/fsearch.htm" ALT="Search this book"></map><!-- TOP NAV BAR --><div class="navbar"><table width="515" border="0"><tr><td align="left" valign="top" width="172"><a href="ch09_02.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0"></a></td><td align="center" valign="top" width="171"><a href="ch09_01.htm">Chapter 9: Data Structures</a></td><td align="right" valign="top" width="172"><a href="ch09_04.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0"></a></td></tr></table></div><hr width="515" align="left"><!-- SECTION BODY --><h2 class="sect1">9.3. Arrays of Hashes</h2><p><a name="INDEX-2127"></a><a name="INDEX-2128"></a><a name="INDEX-2129"></a>An array of hashes is useful when you have a bunch of records thatyou'd like to access sequentially, and each record itself containskey/value pairs. Arrays of hashes are used less frequently than theother structures in this chapter.</p><h3 class="sect2">9.3.1. Composition of an Array of Hashes</h3><p><a name="INDEX-2130"></a>You can create an array of anonymous hashes as follows:<blockquote><pre class="programlisting">@AoH = ( { husband => "barney", wife => "betty", son => "bamm bamm", }, { husband => "george", wife => "jane", son => "elroy", }, { husband => "homer", wife => "marge", son => "bart", }, );</pre></blockquote>To add another hash to the array, you can simply say:<blockquote><pre class="programlisting">push @AoH, { husband => "fred", wife => "wilma", daughter => "pebbles" };</pre></blockquote></p><h3 class="sect2">9.3.2. Generation of an Array of Hashes</h3><p><a name="INDEX-2131"></a><a name="INDEX-2132"></a>Here are some techniques for populating an array of hashes.To read from a file with the following format:<blockquote><pre class="programlisting">husband=fred friend=barney</pre></blockquote>you could use either of the following two loops:<blockquote><pre class="programlisting">while ( <> ) { $rec = {}; for $field ( split ) { ($key, $value) = split /=/, $field; $rec->{$key} = $value; } push @AoH, $rec;}while ( <> ) { push @AoH, { split /[\s=]+/ };}</pre></blockquote>If you have a subroutine <tt class="literal">get_next_pair</tt> that returnskey/value pairs, you can use it to stuff <tt class="literal">@AoH</tt> with either ofthese two loops:<blockquote><pre class="programlisting">while ( @fields = get_next_pair() ) { push @AoH, { @fields };}while (<>) { push @AoH, { get_next_pair($_) };}</pre></blockquote><a name="INDEX-2133"></a>You can append new members to an existing hash like so:<blockquote><pre class="programlisting">$AoH[0]{pet} = "dino";$AoH[2]{pet} = "santa's little helper";</pre></blockquote></p><h3 class="sect2">9.3.3. Access and Printing of an Array of Hashes</h3><p><a name="INDEX-2134"></a><a name="INDEX-2135"></a><a name="INDEX-2136"></a>You can set a key/value pair of a particular hash as follows:<blockquote><pre class="programlisting">$AoH[0]{husband} = "fred";</pre></blockquote>To capitalize the husband of the second array, apply a substitution:<blockquote><pre class="programlisting">$AoH[1]{husband} =~ s/(\w)/\u$1/;</pre></blockquote>You can print all of the data as follows:<blockquote><pre class="programlisting">for $href ( @AoH ) { print "{ "; for $role ( keys %$href ) { print "$role=$href->{$role} "; } print "}\n";}</pre></blockquote>and with indices:<blockquote><pre class="programlisting">for $i ( 0 .. $#AoH ) { print "$i is { "; for $role ( keys %{ $AoH[$i] } ) { print "$role=$AoH[$i]{$role} "; } print "}\n";}</pre></blockquote></p><a name="INDEX-2137"></a><a name="INDEX-2138"></a><a name="INDEX-2139"></a><!-- BOTTOM NAV BAR --><hr width="515" align="left"><div class="navbar"><table width="515" border="0"><tr><td align="left" valign="top" width="172"><a href="ch09_02.htm"><img src="../gifs/txtpreva.gif" alt="Previous" border="0"></a></td><td align="center" valign="top" width="171"><a href="index.htm"><img src="../gifs/txthome.gif" alt="Home" border="0"></a></td><td align="right" valign="top" width="172"><a href="ch09_04.htm"><img src="../gifs/txtnexta.gif" alt="Next" border="0"></a></td></tr><tr><td align="left" valign="top" width="172">9.2. Hashes of Arrays</td><td align="center" valign="top" width="171"><a href="index/index.htm"><img src="../gifs/index.gif" alt="Book Index" border="0"></a></td><td align="right" valign="top" width="172">9.4. Hashes of Hashes</td></tr></table></div><hr width="515" align="left"><!-- LIBRARY NAV BAR --><img src="../gifs/smnavbar.gif" usemap="#library-map" border="0" alt="Library Navigation Links"><p><font size="-1"><a href="copyrght.htm">Copyright © 2001</a> O'Reilly & Associates. All rights reserved.</font></p><map name="library-map"> <area shape="rect" coords="2,-1,79,99" href="../index.htm"><area shape="rect" coords="84,1,157,108" href="../perlnut/index.htm"><area shape="rect" coords="162,2,248,125" href="../prog/index.htm"><area shape="rect" coords="253,2,326,130" href="../advprog/index.htm"><area shape="rect" coords="332,1,407,112" href="../cookbook/index.htm"><area shape="rect" coords="414,2,523,103" href="../sysadmin/index.htm"></map><!-- END OF BODY --></body></html>⌨️ 快捷键说明
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