Re: prograMing: split a list

*To*: mathgroup at smc.vnet.net*Subject*: [mg8955] [mg8893] Re: prograMing: split a list*From*: Leszek Sczaniecki <lsczan at concentric.net>*Date*: Mon, 6 Oct 1997 01:59:23 -0400*Organization*: Concentric Internet Services*Sender*: owner-wri-mathgroup at wolfram.com

What about this solution? In[1]:= myList=Table[Random[Integer,{1,200}],{10000}]; In[2]:= fQ=OddQ; In[3]:= {Select[myList, fQ], Select[myList,!fQ]} ;// Timing Out[3]= {0.15 Second,Null} In[4]:= fQ=OddQ; In[5]:= split1[myList_List, fQ_]:=({Delete[myList,#],Part[myList,Sequence@@#]&/@#}&)@( Position[#,_?fQ,{1}]&)@myList; In[6]:= split2[myList_List, fQ_]:=(Last at Transpose@#&)/@( Split[#,(First at #1===First@#2)&]&)@( Sort[#,OrderedQ at {First@#1,First at #2}&]&)@((List[fQ at #,#]&)/@myList); In[7]:= split3[myList_List, fQ_]:=({Cases[#,False[b_]->b,{1}], Cases[#,True[b_]->b,{1}]}&)@(((fQ[#])@#&)/@myList); In[8]:= solutions={split1,split2,split3}; In[9]:= results=(Timing@(#[myList,fQ]))&/@solutions; In[10]:= {First at #,Equal@@Last at #}&@Transpose at results Out[10]= {{0.601 Second,5.228 Second,0.35 Second},True} - leszek Xah wrote: > Another recreational prograMing problem. > > I want to separate the elements in a given list myList into two groups, > depending on whether the function fQ applied to that element returns True or > False. The desired result list should have the form {{a1,a2,...},{b1,b2...}} > where the first part are elements in myList that fQ returns False. > > For example, suppose myList is a list of positive integers, and fQ is OddQ. > Here are three solutions and their timing. > > Clear[myList,fQ,split1,split2,split3]; > myList=Table[Random[Integer,{1,200}],{1000}]; > fQ=OddQ; > split1[myList_List, > fQ_]:=({Delete[myList,#],Part[myList,Sequence@@#]&/@#}&)@( > Position[#,_?fQ,{1}]&)@myList; > split2[myList_List, > fQ_]:=(Last at Transpose@#&)/@( > Split[#,(First at #1===First@#2)&]&)@( > Sort[#,OrderedQ at {First@#1,First at #2}&]&)@((List[fQ at #,#]&)/@myList); > split3[myList_List, > fQ_]:=({Cases[#,False[b_]->b,{1}], > Cases[#,True[b_]->b,{1}]}&)@(((fQ[#])@#&)/@myList); > > solutions={split1,split2,split3}; > > results=(Timing@(#[myList,fQ]))&/@solutions; > > {First at #,Equal@@Last at #}&@Transpose at results > > {{0.233333 Second,1.53333 Second,0.15 Second},True} > > This is an easy problem with many possible approaches. What I'm looking for > is speed. Can anyone come up with a faster solution? > > Note: There shouldn't be any assumption on the elements of myList and fQ may > be time consuming. The order in myList should be preserved. Also, please > avoid 3.0 funtions such as Extract. > > Xah > xah at best.com > http://www.best.com/~xah/SpecialPlaneCurves_dir/specialPlaneCurves.html > Mountain View, CA, USA