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92 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 SET-DIFFERENCE, NSET-DIFFERENCE</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_pshnew.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_set_ex.htm"><IMG WIDTH=40 HEIGHT=40 ALT="[Next]" SRC="../Graphics/Next.gif" ALIGN=Bottom></A></H1>
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<HR>
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<A NAME="set-difference"><A NAME="nset-difference"><I>Function</I> <B>SET-DIFFERENCE, NSET-DIFFERENCE</B></A></A> <P>
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<P><B>Syntax:</B><P>
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<P>
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<B>set-difference</B> <I>list-1 list-2 <TT>&key</TT> key test test-not</I> => <I>result-list</I><P>
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<B>nset-difference</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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<A REL=DEFINITION HREF="#set-difference"><B>set-difference</B></A> returns a <A REL=DEFINITION HREF="26_glo_l.htm#list"><I>list</I></A> of elements of <I>list-1</I> that do not appear in <I>list-2</I>. <P>
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<A REL=DEFINITION HREF="#nset-difference"><B>nset-difference</B></A> is the destructive version of <A REL=DEFINITION HREF="#set-difference"><B>set-difference</B></A>. It may destroy <I>list-1</I>. <P>
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For all possible ordered pairs consisting of one element from <I>list-1</I> and one element from <I>list-2</I>, the <TT>:test</TT> or <TT>:test-not</TT> function is 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 the part of an element of <I>list-1</I> that is returned by the <TT>:key</TT> function (if supplied); the second argument is the part of an element of <I>list-2</I> that is returned by the <TT>:key</TT> function (if supplied). <P>
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If <TT>:key</TT> is supplied, its argument is a <I>list-1</I> or <I>list-2</I> element. The <TT>:key</TT> function typically returns part of the supplied element. If <TT>:key</TT> is not supplied, the <I>list-1</I> or <I>list-2</I> element is used. <P>
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An element of <I>list-1</I> appears in the result if and only if it does not match any element of <I>list-2</I>. <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 of <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 lst1 (list "A" "b" "C" "d")
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lst2 (list "a" "B" "C" "d")) => ("a" "B" "C" "d")
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(set-difference lst1 lst2) => ("d" "C" "b" "A")
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(set-difference lst1 lst2 :test 'equal) => ("b" "A")
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(set-difference lst1 lst2 :test #'equalp) => NIL
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(nset-difference lst1 lst2 :test #'string=) => ("A" "b")
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(setq lst1 '(("a" . "b") ("c" . "d") ("e" . "f")))
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=> (("a" . "b") ("c" . "d") ("e" . "f"))
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(setq lst2 '(("c" . "a") ("e" . "b") ("d" . "a")))
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=> (("c" . "a") ("e" . "b") ("d" . "a"))
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(nset-difference lst1 lst2 :test #'string= :key #'cdr)
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=> (("c" . "d") ("e" . "f"))
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lst1 => (("a" . "b") ("c" . "d") ("e" . "f"))
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lst2 => (("c" . "a") ("e" . "b") ("d" . "a"))
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</PRE>
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</TT>
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<PRE>
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;; Remove all flavor names that contain "c" or "w".
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(set-difference '("strawberry" "chocolate" "banana"
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"lemon" "pistachio" "rhubarb")
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'(#\c #\w)
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:test #'(lambda (s c) (find c s)))
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=> ("banana" "rhubarb" "lemon") ;One possible ordering.
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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="#nset-difference"><B>nset-difference</B></A> may destroy <I>list-1</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=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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<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><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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