<?xml version="1.0" encoding="utf-8" ?> <!-- for emacs: -*- coding: utf-8 -*- --> <!-- Apache may like this line in the file .htaccess: AddCharset utf-8 .html --> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1 plus MathML 2.0 plus SVG 1.1//EN" "http://www.w3.org/2002/04/xhtml-math-svg/xhtml-math-svg-flat.dtd" > <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"> <head><title>applyPairs -- apply a function to each pair in a hash table</title> <link rel="stylesheet" type="text/css" href="../../../../Macaulay2/Style/doc.css"/> </head> <body> <table class="buttons"> <tr> <td><div><a href="_merge_lp__Hash__Table_cm__Hash__Table_cm__Function_rp.html">next</a> | <a href="_apply__Values.html">previous</a> | <a href="_merge_lp__Hash__Table_cm__Hash__Table_cm__Function_rp.html">forward</a> | <a href="_apply__Values.html">backward</a> | <a href="_hash_sptables.html">up</a> | <a href="index.html">top</a> | <a href="master.html">index</a> | <a href="toc.html">toc</a> | <a href="http://www.math.uiuc.edu/Macaulay2/">Macaulay2 web site</a></div> </td> </tr> </table> <div><a href="index.html" title="">Macaulay2Doc</a> > <a href="___The_sp__Macaulay2_splanguage.html" title="">The Macaulay2 language</a> > <a href="_hash_sptables.html" title="">hash tables</a> > <a href="_apply__Pairs.html" title="apply a function to each pair in a hash table">applyPairs</a></div> <hr/> <div><h1>applyPairs -- apply a function to each pair in a hash table</h1> <div class="single"><h2>Synopsis</h2> <ul><li><div class="list"><dl class="element"><dt class="heading">Usage: </dt><dd class="value"><div><tt>applyPairs(H,f)</tt></div> </dd></dl> </div> </li> <li><div class="single">Inputs:<ul><li><span><tt>H</tt>, <span>a <a href="___Hash__Table.html">hash table</a></span></span></li> <li><span><tt>f</tt>, <span>a <a href="___Function.html">function</a></span>, with two arguments, returning a pair or <a href="_null.html" title="the unique member of the empty class">null</a></span></li> </ul> </div> </li> <li><div class="single">Outputs:<ul><li><span><span>a <a href="___Hash__Table.html">hash table</a></span></span></li> </ul> </div> </li> </ul> </div> <div class="single"><h2>Description</h2> <div>The result of <tt>applyPairs(H,f)</tt> is a new hash table obtained by applying the function <tt>f</tt> to each key/value pair <tt>(k,v)</tt> in <tt>H</tt> and storing the resulting key/value pair in the new hash table. If the function returns <a href="_null.html" title="the unique member of the empty class">null</a> then no action is performed.<p/> In this example, we show how to produce the hash table corresponding to the inverse of a function.<table class="examples"><tr><td><pre>i1 : x = new HashTable from {1 => a, 2 => b, 3 => c} o1 = HashTable{1 => a} 2 => b 3 => c o1 : HashTable</pre> </td></tr> <tr><td><pre>i2 : y = applyPairs(x, (k,v) -> (v,k)) o2 = HashTable{a => 1} b => 2 c => 3 o2 : HashTable</pre> </td></tr> <tr><td><pre>i3 : x#2 o3 = b o3 : Symbol</pre> </td></tr> <tr><td><pre>i4 : y#b o4 = 2</pre> </td></tr> </table> </div> </div> <div class="single"><h2>Caveat</h2> <div>It is an error for the function <tt>f</tt> to return two pairs with the same key.</div> </div> <div class="single"><h2>See also</h2> <ul><li><span><a href="_apply__Keys.html" title="apply a function to each key in a hash table">applyKeys</a> -- apply a function to each key in a hash table</span></li> <li><span><a href="_apply__Values.html" title="apply a function to each value">applyValues</a> -- apply a function to each value</span></li> <li><span><a href="_scan__Pairs.html" title="apply a function to pairs in a hash table">scanPairs</a> -- apply a function to pairs in a hash table</span></li> </ul> </div> <div class="waystouse"><h2>Ways to use <tt>applyPairs</tt> :</h2> <ul><li>applyPairs(HashTable,Function)</li> </ul> </div> </div> </body> </html>