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86 lines
9.5 KiB
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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 INTERSECTION, NINTERSECTION</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="m_remf.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_adjoin.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<A NAME="intersection"><A NAME="nintersection"><I>Function</I> <B>INTERSECTION, NINTERSECTION</B></A></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>intersection</B> <I>list-1 list-2 <TT>&key</TT> key test test-not</I> => <I>result-list</I><P>
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<B>nintersection</B> <I>list-1 list-2 <TT>&key</TT> key test test-not</I> => <I>result-list</I><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>list-1</I>---a <A REL=DEFINITION HREF="26_glo_p.htm#proper_list"><I>proper list</I></A>. <P>
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<I>list-2</I>---a <A REL=DEFINITION HREF="26_glo_p.htm#proper_list"><I>proper list</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>result-list</I>---a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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<A REL=DEFINITION HREF="#intersection"><B>intersection</B></A> and <A REL=DEFINITION HREF="#nintersection"><B>nintersection</B></A> return a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> that contains every element that occurs in both <I>list-1</I> and <I>list-2</I>. <P>
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<A REL=DEFINITION HREF="#nintersection"><B>nintersection</B></A> is the destructive version of <A REL=DEFINITION HREF="#intersection"><B>intersection</B></A>. It performs the same operation, but may destroy <I>list-1</I> using its cells to construct the result. <I>list-2</I> is not destroyed. <P>
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The intersection operation is described as follows. For all possible ordered pairs consisting of one <A REL=DEFINITION HREF="26_glo_e.htm#element"><I>element</I></A> from <I>list-1</I> and one <A REL=DEFINITION HREF="26_glo_e.htm#element"><I>element</I></A> from <I>list-2</I>, <TT>:test</TT> or <TT>:test-not</TT> are used to determine whether they <A REL=DEFINITION HREF="26_glo_s.htm#satisfy_the_test"><I>satisfy the test</I></A>. The first argument to the <TT>:test</TT> or <TT>:test-not</TT> function is an element of <I>list-1</I>; the second argument is an element of <I>list-2</I>. If <TT>:test</TT> or <TT>:test-not</TT> is not supplied, <A REL=DEFINITION HREF="f_eql.htm#eql"><B>eql</B></A> is used. It is an error if <TT>:test</TT> and <TT>:test-not</TT> are supplied in the same function call. <P>
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If <TT>:key</TT> is supplied (and not <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>), it is used to extract the part to be tested from the <I>list</I> element. The argument to the <TT>:key</TT> function is an element of either <I>list-1</I> or <I>list-2</I>; the <TT>:key</TT> function typically returns part of the supplied element. If <TT>:key</TT> is not supplied or <A REL=DEFINITION HREF="a_nil.htm#nil"><B>nil</B></A>, the <I>list-1</I> and <I>list-2</I> elements are used. <P>
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For every pair that <I>satifies the test</I>, exactly one of the two elements of the pair will be put in the result. No element from either <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> appears in the result that does not <A REL=DEFINITION HREF="26_glo_s.htm#satisfy_the_test"><I>satisfy the test</I></A> for an element from the other <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A>. If one of the <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>lists</I></A> contains duplicate elements, there may be duplication in the result. <P>
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There is no guarantee that the order of elements in the result will reflect the ordering of the arguments in any particular way. The result <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> may share cells with, or be <A REL=DEFINITION HREF="f_eq.htm#eq"><B>eq</B></A> to, either <I>list-1</I> or <I>list-2</I> if appropriate. <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 list1 (list 1 1 2 3 4 a b c "A" "B" "C" "d")
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list2 (list 1 4 5 b c d "a" "B" "c" "D"))
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=> (1 4 5 B C D "a" "B" "c" "D")
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(intersection list1 list2) => (C B 4 1 1)
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(intersection list1 list2 :test 'equal) => ("B" C B 4 1 1)
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(intersection list1 list2 :test #'equalp) => ("d" "C" "B" "A" C B 4 1 1)
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(nintersection list1 list2) => (1 1 4 B C)
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list1 => <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent">implementation-dependent</A> ;e.g., (1 1 4 B C)
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list2 => <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent">implementation-dependent</A> ;e.g., (1 4 5 B C D "a" "B" "c" "D")
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(setq list1 (copy-list '((1 . 2) (2 . 3) (3 . 4) (4 . 5))))
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=> ((1 . 2) (2 . 3) (3 . 4) (4 . 5))
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(setq list2 (copy-list '((1 . 3) (2 . 4) (3 . 6) (4 . 8))))
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=> ((1 . 3) (2 . 4) (3 . 6) (4 . 8))
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(nintersection list1 list2 :key #'cdr) => ((2 . 3) (3 . 4))
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list1 => <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent">implementation-dependent</A> ;e.g., ((1 . 2) (2 . 3) (3 . 4))
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list2 => <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent">implementation-dependent</A> ;e.g., ((1 . 3) (2 . 4) (3 . 6) (4 . 8))
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</PRE>
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</TT> <P>
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<P><B>Side Effects:</B><P>
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<P>
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<A REL=DEFINITION HREF="#nintersection"><B>nintersection</B></A> can modify <I>list-1</I>, but not <I>list-2</I>. <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><P>
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<P>
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Should be prepared to signal an error of <A REL=DEFINITION HREF="26_glo_t.htm#type"><I>type</I></A> <A REL=DEFINITION HREF="e_tp_err.htm#type-error"><B>type-error</B></A> if <I>list-1</I> and <I>list-2</I> are not <A REL=DEFINITION HREF="26_glo_p.htm#proper_list"><I>proper lists</I></A>. <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_unionc.htm#union"><B>union</B></A>, <A REL=CHILD HREF="03_ba.htm">Section 3.2.1 (Compiler Terminology)</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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Since the <A REL=DEFINITION HREF="#nintersection"><B>nintersection</B></A> side effect is not required, it should not be used in for-effect-only positions in portable code. <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/iss083.htm">CONSTANT-MODIFICATION:DISALLOW</A><LI> <A REL=CHILD HREF="../Issues/iss247.htm">NINTERSECTION-DESTRUCTION</A><LI> <A REL=CHILD HREF="../Issues/iss293.htm">REMF-DESTRUCTION-UNSPECIFIED:X3J13-MAR-89</A><LI> <A REL=CHILD HREF="../Issues/iss248.htm">NINTERSECTION-DESTRUCTION:REVERT</A><P></UL><HR>
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<A REL=NAVIGATOR HREF="../Front/StartPts.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Starting Points]" SRC="../Graphics/StartPts.gif" ALIGN=Bottom></A><A REL=TOC HREF="../Front/Contents.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Contents]" SRC="../Graphics/Contents.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Master.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Index]" SRC="../Graphics/Index.gif" ALIGN=Bottom></A><A REL=INDEX HREF="../Front/X_Symbol.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Symbols]" SRC="../Graphics/Symbols.gif" ALIGN=Bottom></A><A REL=GLOSSARY HREF="../Body/26_a.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Glossary]" SRC="../Graphics/Glossary.gif" ALIGN=Bottom></A><A HREF="../Front/X3J13Iss.htm"><IMG WIDTH=80 HEIGHT=40 ALT="[Issues]" SRC="../Graphics/Issues.gif" ALIGN=Bottom></A><BR>
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<A REL=COPYRIGHT HREF="../Front/Help.htm#Legal"><I>Copyright 1996-2005, LispWorks Ltd. All rights reserved.</I></A><P>
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