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MathGroup Archive 2002

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RE: Re: Pattern Matching in Lists

  • To: mathgroup at smc.vnet.net
  • Subject: [mg35617] RE: [mg35596] Re: Pattern Matching in Lists
  • From: "DrBob" <majort at cox-internet.com>
  • Date: Tue, 23 Jul 2002 01:51:16 -0400 (EDT)
  • Reply-to: <drbob at bigfoot.com>
  • Sender: owner-wri-mathgroup at wolfram.com

f6 appears to be about twice as fast as f4:

Needs["Statistics`HypothesisTests`"]
f1[w_] := Count[Partition[w, 2, 1], {1, 0}]
f2[w_] := Count[Drop[w, -1] - Drop[w, 1], 1]
f3[w_] := Count[Drop[w + 2RotateRight[w], 1], 2]
f4[w_] := Tr[Drop[w, -1](Drop[w, -1] - Drop[w, 1])]
f5[w_] := (Tr[w] - Tr[BitAnd[w, RotateLeft[w]]]) + If[w[[
    1]] == 0 && w[[-1]] == 1, -1, 0]
f6[w_] := (Tr[#] - Tr[# Drop[w, 1]]) &[Drop[w, -1]]
trial := (n = 2000000; w = Table[Random[Integer], {n}];
First@Timing[#[w];]/Second & /@ {f4, f6}
    )

{t1, t2} = Transpose[trial & /@ Range[30]];
Mean /@ {t1, t2}
r = MeanTest[t1 - t2, 0, FullReport -> True]
meanDiff = (FullReport /. r)[[1, 1, 1]];
Print["% difference = ", meanDiff/Mean[t1]]

{0.21726666666666658, 0.11146666666666712}
{FullReport -> TableForm[
    {{"Mean", "TestStat", "Distribution"}, 
     {0.10579999999999945, 15.693202721924115, 
      StudentTDistribution[29]}}, 
    TableHeadings -> 
     {None, {"Mean", "TestStat", "Distribution"}}], 
  OneSidedPValue -> 5.207406739210963*^-16}

% difference = 0.4869591899

f5 is still about 1.5 times as fast as f6, though:

trial := (n = 2000000; w = Table[Random[Integer], {n}];
First@Timing[#[w];]/Second & /@ {f6, f5}
    )

(same test code as above)

{0.09896666666666647, 0.0691333333333335}
{FullReport -> TableForm[
 {{"Mean", "TestStat", "Distribution"}, 
 {0.029833333333332965, 5.308061210842354, StudentTDistribution[29]}}, 
  TableHeadings -> {None, {"Mean", "TestStat", "Distribution"}}], 
  OneSidedPValue -> 5.387889994701921*^-6}
% difference = 0.3014482990

Bobby Treat

-----Original Message-----
From: Allan Hayes [mailto:hay at haystack.demon.co.uk] 
To: mathgroup at smc.vnet.net
Subject: [mg35617] [mg35596] Re: Pattern Matching in Lists

Carl,
Pushing your idea a bit further and avoiding one Drop and a subtraction
of
lists:

    w=Table[Random[Integer],{1000000}];

    Tr[Drop[w,-1](Drop[w,-1]-Drop[w,1])]//Timing

        {7.85 Second,249850}

    (Tr[#]-Tr[# Drop[w,1]])&[Drop[w,-1] ]//Timing

        {2.75 Second,249850}

--
Allan

---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565


"Carl K. Woll" <carlw at u.washington.edu> wrote in message
news:ahdfd2$i3i$1 at smc.vnet.net...
> Anthony and newsgroup,
>
> I thought of another method of  solving this problem which is 5 or 6
times
> faster than my previous version. Here is a test case.
>
> tst=Table[Random[Integer],{1000000}];
>
> My first solution was
>
> In[16]:=
> Count[Partition[tst,2,1],{1,0}]//Timing
> Out[16]=
> {0.704 Second, 249722}
>
> My second solution is
>
> In[17]:=
> Tr[Drop[tst,-1](Drop[tst,-1]-Drop[tst,1])]//Timing
> Out[17]=
> {0.125 Second, 249722}
>
> Carl Woll
> Physics Dept
> U of Washington
>
> "Anthony Mendes" <amendes at zeno.ucsd.edu> wrote in message
> news:ah5qce$59o$1 at smc.vnet.net...
> >Hello,
> >
> > Suppose w={1,1,1,0,0,1,0,1,0,0,1,0,0}.
> >
> > How can I count the number of occurrences of a 1 in w immediately
> > followed by a 0 in w?
> >
> > I have tried every incarnation of Count[] I can think of; for
example,
> >
> > Count[w,{___,1,0,___}]
> >
> > does not seem to work.  In general, how can I count the number of
> > occurrences of a 1 followed by a 0 in a list of 1's and 0's?  Thank
you!
> >
> >
> > --
> > Tony
> > _____________________
> > amendes at math.ucsd.edu
> >
> >
> >
> >
>
>
>







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