Re: Better way to write this
- To: mathgroup at smc.vnet.net
- Subject: [mg85083] Re: Better way to write this
- From: "Steve Luttrell" <steve at _removemefirst_luttrell.org.uk>
- Date: Sun, 27 Jan 2008 05:49:15 -0500 (EST)
- References: <fnet45$id5$1@smc.vnet.net>
Tally gives the number of times each element of a list occurs, then pick out
the cases that occur only once.
Here is an example:
data = RandomInteger[{1, 100}, {250}];
Cases[Tally[data], {x_, 1} :> x]
Stephen Luttrell
West malvern, UK
"Louis Theran" <theran at gmail.com> wrote in message
news:fnet45$id5$1 at smc.vnet.net...
>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
>