Re: fast summing alternative?

*To*: mathgroup at smc.vnet.net*Subject*: [mg128358] Re: fast summing alternative?*From*: Roland Franzius <roland.franzius at uos.de>*Date*: Tue, 9 Oct 2012 00:39:48 -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*References*: <k4tth1$sgq$1@smc.vnet.net>

Am 08.10.2012 08:57, schrieb Chris: > Dear all > > The code below is part of a large compile function I wrote and the inputs, like the matrices weights and newData, are in fact large data files. Thus, I provide them in the following problem as random. Although, written as compile code (with CompilationTarget->"C") it is still too slow for the amounts of data I have to process. I provide two of my fastest alternatives, which sadly are not that fast. I do appreciate any help to make the code faster. Thanks in advance! > > > (* > What I do is simple: For each row of newMat and weights I construct a new row. The elements of this new row are the sums of the elements in weights if a certain requirement of the same element in newMat is met. > *) > > Clear[bNum,nNum,weights,newMat,sortMat,tab]; > > bNum; Number missing bNum=100; > nNum=100; > > weights=Table[RandomReal[{-10,10}],{b,1,bNum},{n,1,nNum}]; > newMat=Table[RandomReal[{-10,10}],{b,1,bNum},{n,1,nNum}]; > sortMat=Table[i,{i, -10, 10, 0.1}]; (*elements always evenly spaced*) > > (*first alternative*) > tab=Table[ > Sum[weights[[k,i]]*If[newMat[[k,i]] <= sortMat[[j]],1.,0.],{i,1,nNum}],{k,1,bNum}, > {j,1,Length[sortMat]}];//AbsoluteTiming > {3.9624069, Null} > (*second alternative*) > mat=Block[{k=1}, > Reap[Do[ > Sow[Table[Sum[weights[[k,i]]*If[newMat[[k,i]] <= sortMat[[j]],1.,0.],{i,1,nNum}],{j,1,Length[sortMat]}]]; > k++,{bNum}]]][[2,1]];//AbsoluteTiming > {3.9624069, Null} List manipulations without references to elements and Replace instead of If's will save you more than half of the time ((projector = Outer[ #1 >= #2 &, sortMat, newMat] /. {True -> 1, False -> 0}); pw = Plus @@@ Transpose[ Map[(Plus @@ (weights*#) &), projector]];) // AbsoluteTiming {1.5288027, Null} I only checked dimensions of arrays for a short run time check. The correct use of Outer, Transpose and element multiplication is up to you. For Plus@@@ a*b for vectors you can use Dot or Inner instead -- Roland Franzius