Re: Better way to write this
- To: mathgroup at smc.vnet.net
- Subject: [mg85084] Re: [mg85058] Better way to write this
- From: Murray Eisenberg <murray at math.umass.edu>
- Date: Sun, 27 Jan 2008 05:49:46 -0500 (EST)
- Organization: Mathematics & Statistics, Univ. of Mass./Amherst
- References: <200801261000.FAA21110@smc.vnet.net>
- Reply-to: murray at math.umass.edu
Try the following:
listUnique[lis_List] := Pick[lis, (Count[lis,#]==1)& /@ lis]
For example:
lis1 = {a, b, b, c};
lis2 = {x, x, y, z, x, w};
listUnique /@ {lis1, lis2}
{{a,c},{y,z,w}}
I haven't checked timings, but in general it's a good idea to exploit
kernel functions that work on whole lists at once, e.g., Pick and Count.
Louis Theran wrote:
> I have the following function that takes as its input a number of
> lists and returns the elements in each of them that appear exactly
> once:
>
> SpecialElements[lists:_List..]:=
> Module[{l,n,Sower,Reaper},
> l = {lists}; n = Length[l];
> Sower[l_,{idx_}]:= Sow[idx,{#}] & /@ l;
> Reaper[val_,{place_}] := Sow[val,place];
> Reaper[val_,x_]:= Null;
> Reap[Reap[MapIndexed[Sower, l],_,Reaper],Range[n]][[2]]]
>
> This works pretty well, but since I am using it on rather large
> inputs, I was wondering if there is a faster way to implement it than
> Reap/Sow, which is sort of counting in unary.
>
> ^L
>
--
Murray Eisenberg murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower phone 413 549-1020 (H)
University of Massachusetts 413 545-2859 (W)
710 North Pleasant Street fax 413 545-1801
Amherst, MA 01003-9305
- References:
- Better way to write this
- From: Louis Theran <theran@gmail.com>
- Better way to write this