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90 lines
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<!-- Common Lisp HyperSpec (TM), version 7.0 generated by Kent M. Pitman on Mon, 11-Apr-2005 2:31am EDT -->
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<TITLE>CLHS: Function RASSOC, RASSOC-IF, RASSOC-IF-NOT</TITLE>
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<H1><A REV=MADE HREF="http://www.lispworks.com/"><IMG WIDTH=80 HEIGHT=65 ALT="[LISPWORKS]" SRC="../Graphics/LWSmall.gif" ALIGN=Bottom></A><A REL=TOP HREF="../Front/index.htm"><IMG WIDTH=237 HEIGHT=65 ALT="[Common Lisp HyperSpec (TM)]" SRC="../Graphics/CLHS_Sm.gif" ALIGN=Bottom></A> <A REL=PREV HREF="f_pairli.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Previous]" SRC="../Graphics/Prev.gif" ALIGN=Bottom></A><A REL=UP HREF="c_conses.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Up]" SRC="../Graphics/Up.gif" ALIGN=Bottom></A><A REL=NEXT HREF="f_get_pr.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="rassoc"><A NAME="rassoc-if"><A NAME="rassoc-if-not"><I>Function</I> <B>RASSOC, RASSOC-IF, RASSOC-IF-NOT</B></A></A></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>rassoc</B> <I>item alist <TT>&key</TT> key test test-not</I> => <I>entry</I><P>
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<P>
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<P>
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<B>rassoc-if</B> <I>predicate alist <TT>&key</TT> key</I> => <I>entry</I><P>
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<B>rassoc-if-not</B> <I>predicate alist <TT>&key</TT> key</I> => <I>entry</I><P>
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<P>
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<P>
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<P><B>Arguments and Values:</B><P>
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<P>
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<I>item</I>---an <A REL=DEFINITION HREF="26_glo_o.htm#object"><I>object</I></A>. <P>
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<I>alist</I>---an <A REL=DEFINITION HREF="26_glo_a.htm#association_list"><I>association list</I></A>. <P>
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<I>predicate</I>---a <A REL=DEFINITION HREF="26_glo_d.htm#designator"><I>designator</I></A> for a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> of one <A REL=DEFINITION HREF="26_glo_a.htm#argument"><I>argument</I></A> that returns a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. <P>
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<I>test</I>---a <A REL=DEFINITION HREF="26_glo_d.htm#designator"><I>designator</I></A> for a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> of two <A REL=DEFINITION HREF="26_glo_a.htm#argument"><I>arguments</I></A> that returns a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. <P>
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<I>test-not</I>---a <A REL=DEFINITION HREF="26_glo_d.htm#designator"><I>designator</I></A> for a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> of two <A REL=DEFINITION HREF="26_glo_a.htm#argument"><I>arguments</I></A> that returns a <A REL=DEFINITION HREF="26_glo_g.htm#generalized_boolean"><I>generalized boolean</I></A>. <P>
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<I>key</I>---a <A REL=DEFINITION HREF="26_glo_d.htm#designator"><I>designator</I></A> for a <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> of one argument, or <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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<I>entry</I>---a <A REL=DEFINITION HREF="26_glo_c.htm#cons"><I>cons</I></A> that is an <A REL=DEFINITION HREF="26_glo_e.htm#element"><I>element</I></A> of the <I>alist</I>, or <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#rassoc"><B>rassoc</B></A>, <A REL=DEFINITION HREF="#rassoc-if"><B>rassoc-if</B></A>, and <A REL=DEFINITION HREF="#rassoc-if-not"><B>rassoc-if-not</B></A> return the first <A REL=DEFINITION HREF="26_glo_c.htm#cons"><I>cons</I></A> whose <A REL=DEFINITION HREF="26_glo_c.htm#cdr"><I>cdr</I></A> <I>satisfies the test</I>. If no such <A REL=DEFINITION HREF="26_glo_c.htm#cons"><I>cons</I></A> is found, <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A> s returned. <P>
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<P>
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If <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A> appears in <I>alist</I> in place of a pair, it is ignored. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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(setq alist '((1 . "one") (2 . "two") (3 . 3)))
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=> ((1 . "one") (2 . "two") (3 . 3))
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(rassoc 3 alist) => (3 . 3)
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(rassoc "two" alist) => NIL
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(rassoc "two" alist :test 'equal) => (2 . "two")
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(rassoc 1 alist :key #'(lambda (x) (if (numberp x) (/ x 3)))) => (3 . 3)
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(rassoc 'a '((a . b) (b . c) (c . a) (z . a))) => (C . A)
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(rassoc-if #'stringp alist) => (1 . "one")
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(rassoc-if-not #'vectorp alist) => (3 . 3)
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B> None.
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<P>
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<P><B>Affected By:</B> None.
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<P>
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<P><B>Exceptional Situations:</B> None.
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<P>
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<P><B>See Also:</B><P>
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<P>
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<A REL=DEFINITION HREF="f_assocc.htm#assoc"><B>assoc</B></A>, <A REL=CHILD HREF="03_f.htm">Section 3.6 (Traversal Rules and Side Effects)</A> <P>
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<P><B>Notes:</B><P>
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<P>
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The <TT>:test-not</TT> parameter is deprecated. <P>
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The <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <A REL=DEFINITION HREF="#rassoc-if-not"><B>rassoc-if-not</B></A> is deprecated. <P>
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It is possible to <A REL=DEFINITION HREF="f_rplaca.htm#rplaca"><B>rplaca</B></A> the result of <A REL=DEFINITION HREF="#rassoc"><B>rassoc</B></A>, provided that it is not <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>, in order to ``update'' <I>alist</I>. <P>
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The expressions <P>
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<PRE>
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(rassoc item list :test fn)
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</PRE>
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</TT> and <P>
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<PRE>
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(find item list :test fn :key #'cdr)
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</PRE>
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</TT> are equivalent in meaning, except when the <TT>item</TT> is <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A> nd <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A> appears in place of a pair in the <I>alist</I>. See the <A REL=DEFINITION HREF="26_glo_f.htm#function"><I>function</I></A> <A REL=DEFINITION HREF="f_assocc.htm#assoc"><B>assoc</B></A>. <P>
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<P><HR>The following <A REL=META HREF="../Front/X3J13Iss.htm">X3J13 cleanup issues</A>, <I>not part of the specification</I>, apply to this section:<P><UL><LI> <A REL=CHILD HREF="../Issues/iss345.htm">TEST-NOT-IF-NOT:FLUSH-ALL</A><LI> <A REL=CHILD HREF="../Issues/iss240.htm">MAPPING-DESTRUCTIVE-INTERACTION:EXPLICITLY-VAGUE</A><LI> <A REL=CHILD HREF="../Issues/iss017.htm">ASSOC-RASSOC-IF-KEY</A><LI> <A REL=CHILD HREF="../Issues/iss018.htm">ASSOC-RASSOC-IF-KEY:YES</A><P></UL><HR>
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