Re: Group and Replace itens sequence in a list

*To*: mathgroup at smc.vnet.net*Subject*: [mg127880] Re: Group and Replace itens sequence in a list*From*: Dana DeLouis <dana01 at me.com>*Date*: Wed, 29 Aug 2012 01:14:05 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net

Hi. Just an observation on Fred's excellent code. Just want to post the question on what to do about Overlap. ( ie a,b,a,b,a) v={1,2,3,a,b,a,4,5,6,a,b,c,7,8,9,a,b,a,10,11,12}; vv=Flatten[Table[v,{500}],1]; // OK when there is no overlap g[v] {{1,2,3},{4,5,6,a,b,c,7,8,9},{10,11,12}} // Error with overlap g[{a,b,a,b,a,1,2,3}] Take::take: Cannot take positions 4 through 2 in {a,b,a,b,a,1,2,3}. >> {{},Take[{a,b,a,b,a,1,2,3},{4,2}],{1,2,3}} This idea just deletes them all: Fx[v_List,Patt_List]:=Module[{k,p}, k=Length[Patt]; p=ListConvolve[Patt,v,{-1,1},Null,SameQ,And]; p=Position[p,True]; Do[p=Join[p,p+1],{k-1}]; p=Union[p]; Delete[v,p] ] // This idea deletes them all Fx[{a,b,a,b,a,1,2,3},{a,b,a}] {1,2,3} // I get the same timing on the larger list: g[vv]//Timing//First 0.015412 // A negligible speed improvement. Fx[vv,{a,b,a}]//Timing//First 0.012741 // With same results as your: Flatten[g[vv]]==Fx[vv,{a,b,a}] True = = = = = = = = = = HTH :>) Dana DeLouis Mac & Mathematica 8 = = = = = = = = = = On Saturday, August 25, 2012 4:26:30 AM UTC-4, Fred Simons wrote: > Solutions with pattern matching can be very elegant, such as Bob > > Hanlon's solution, but also tend to be very slow when the problem is a > > little bit larger. > > > > Here is a solution by finding the position of the triple {a,b,a} and > > then taking the parts of the list outside these triples. > > g[lst_] := With[{limits=Partition[Flatten[{1, > > Position[Partition[lst,3,1], {a,b,a}] /. > > {n_Integer}->{n-1,n+3},Length[lst]}],2]}, Take[lst, #]& /@ limits] > > > > In the following commands f is Bob's function: > > > > In[4]:= lst={1,2,3,a,b,a,4,5,6,a,b,c,7,8,9,a,b,a,10,11,12} ; > > z1=f[lst]; // Timing > > z2=g[lst]; // Timing > > z1===z2 > > Out[5]= {0.,Null} > > Out[6]= {0.,Null} > > Out[7]= True > > > > Both functions are fast enough. Now we make the list 500 times longer: > > > > In[12]:= lstt=Flatten[Table[lst, {500}],1]; > > z1=f[lstt]; // Timing > > z2=g[lstt]; // Timing > > z1===z2 > > Out[13]= {5.007632,Null} > > Out[14]= {0.015600,Null} > > Out[15]= True > > > > Fred Simons > > Eindhoven University of Technology > > > > > > Op 24-8-2012 11:04, Bob Hanlon schreef: > > > Clear[f] > > > > > > f[list_?VectorQ] := Cases[ > > > (list //. {s___, a, b, a, r___} -> {{s}, {r}}) /. > > > {} -> > > > Sequence[], _?VectorQ, Infinity] > > > > > > f[{1, 2, 3, a, b, a, 4, 5, 6, a, b, c, 7, 8, 9, a, b, a, 10, 11, 12}] > > > > > > {{1, 2, 3}, {4, 5, 6, a, b, c, 7, 8, 9}, {10, 11, 12}} > > > > > > f[{a, b, a, 1, 2, 3, a, b, a, 4, 5, 6, a, b, c, 7, 8, 9, a, b, a, 10, > > > 11, 12}] > > > > > > {{1, 2, 3}, {4, 5, 6, a, b, c, 7, 8, 9}, {10, 11, 12}} > > > > > > f[{1, 2, 3, a, b, a, 4, 5, 6, a, b, c, 7, 8, 9, a, b, a, 10, 11, 12, > > > a, b, a}] > > > > > > {{1, 2, 3}, {4, 5, 6, a, b, c, 7, 8, 9}, {10, 11, 12}} > > > > > > f[{a, b, a, 1, 2, 3, a, b, a, 4, 5, 6, a, b, c, 7, 8, 9, a, b, a, 10, > > > 11, 12, a, b, a}] > > > > > > {{1, 2, 3}, {4, 5, 6, a, b, c, 7, 8, 9}, {10, 11, 12}} > > > > > > > > > Bob Hanlon > > > > > > > > > On Thu, Aug 23, 2012 at 2:52 AM, Murta <rodrigomurtax at gmail.com> wrote: > > >> Hi All > > >> > > >> I have a simple problem that is: > > >> > > >> l={1,2,3,a,b,a,4,5,6,a,b,c,7,8,9,a,b,a,10,11,12} > > >> > > >> I want to replace all a,b,a sequence by X to get: > > >> > > >> l={1,2,3,X,4,5,6,a,b,7,8,9,X,10,11,12} > > >> > > >> Then I want to group it by X intervals as > > >> l={{1,2,3},{4,5,6,a,b,7,8,9},{10,11,12}} > > >> > > >> If I don't need to put the intermediate X, even better! > > >> I think the with pattern, RaplaceAll and DeleteCases I can do It. Some clue? > > >> Tks > > >> Murta > > >> > > >> > > >> > > > > > > > > > ----- > > > Geen virus gevonden in dit bericht. > > > Gecontroleerd door AVG - www.avg.com > > > Versie: 2012.0.2197 / Virusdatabase: 2437/5219 - datum van uitgifte: 08/23/12 > > > > > > > > >