Re: Unsorted Union
- To: mathgroup at smc.vnet.net
- Subject: [mg61494] Re: Unsorted Union
- From: Konstantin L Kouptsov <klk206 at panix.com>
- Date: Wed, 19 Oct 2005 23:08:14 -0400 (EDT)
- References: <dj4p6t$gpt$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Robert Schoefbeck wrote:
> Hello all,
>
> in the help section i found the following thing:
>
> UnsortedUnion[x_] := Module[{f}, f[y_] := (f[y] = Sequence[]; y); f/@x]
>
> It does just what it says:
> UnsortedUnion[{a,c,b,d,a,b}]={a,c,b,d}
>
> (ordinary Union would Sort the result)
>
> my question is: How does the definition work? I know all the syntax
> and i have been using these concepts for for some time now. But i cant
> figure out what this definition does.
>
> Robert
>
Actually, it soes not:
In[2]:= UnsortedUnion[{a, b, c, c, c, c, b}]
Out[2]:= {a,b,c}