Re: Extract values and multilpicities from list

*To*: mathgroup at smc.vnet.net*Subject*: [mg64943] Re: Extract values and multilpicities from list*From*: Bill Rowe <readnewsciv at earthlink.net>*Date*: Wed, 8 Mar 2006 01:00:20 -0500 (EST)*Sender*: owner-wri-mathgroup at wolfram.com

On 3/7/06 at 6:11 AM, carlw at wolfram.com (Carl K. Woll) wrote: >For the special case where the integers are positive and not too >large, then the following approach is probably close to the >fastest. >runs[d_] := >SparseArray[Transpose[{d, Range[Length[d]]}] -> Table[1, >{Length[d]}]] /. SparseArray[_, _, _, {_, {p_, __}, _}] :> >Transpose[{Range[Length[p] - 1], Rest[p] - Most[p]}] >The simplest solution is probably: >runs2[d_] := {First[#], Length[#]} & /@ Split[Sort[d]] >The output of runs will include integers with 0 length runs, so we >need to eliminate them when comparing results: >In[22]:= r1=runs[data];//Timing r2=runs2[data];//Timing >DeleteCases[r1,{_,0}]===r2 >Out[22]= {0.485 Second,Null} >Out[23]= {0.781 Second,Null} >Out[24]= True What can be accomplished using SparseArray seems to me quite amazing. But in this case (on my machine at least) the simpler runs2 executes faster. That is In[69]:= RandomSeed[0]; n=100000; test=Table[Random[Integer,{1,1000}],{n}]; Timing[r1=runs[test];] Timing[r2=runs2[test];] Out[72]= {0.08321 Second,Null} Out[73]= {0.072016 Second,Null} -- To reply via email subtract one hundred and four