Re: Summing list subsets
- To: mathgroup at smc.vnet.net
- Subject: [mg30738] Re: Summing list subsets
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Sun, 9 Sep 2001 03:26:28 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <9ncfgn$prb$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
is is not clear what you mean in general bu for your
example the command
{First[First[#]], Plus @@ (Last /@ #)} & /@
Split[Transpose[{x, y}], (First[#1] === First[#2] ) &]
work.
Regards
Jens
Mark Coleman wrote:
>
> Greetings:
>
> Consider two lists:
>
> x = {a,a,b,b,b,b,c,d,d,d,d,d,} and y = {1,1,2,2,2,2,3,4,4,4,4,4}
>
> I would like to have a function that returns the sum (or any other function)
> of each unique element of x, given the corresponding value in y. That is,
> for a 'Sum', the result would be
>
> z={{a,2},{b,8},{c,3},{d,20}}
>
> This is similar in spirit to a common database aggregation problem.
>
> Any ideas?
>
> Thanks.
>
> -Mark