Re: Lists and rules
- To: mathgroup at smc.vnet.net
- Subject: [mg66518] Re: Lists and rules
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Wed, 17 May 2006 03:30:55 -0400 (EDT)
- Organization: The Open University, Milton Keynes, UK
- References: <e4bj1m$1b9$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Thomas Schmelzer wrote:
> Experts,
> I would like to produce a decent piece of code for one of my projects.
> I am constructing a list of sets
>
> S_1, S_2 and S_3
>
> where S_j = { m , T[[1,m]] == j, m running from 1 to 100}
>
> T[[1,*]] is a row vector containing only 1, 2 and 3.
>
> I could setup a for loop and work with append. I have done that, but I
> believe this approach is neither efficient nor elegant. Any hints for a
> newbie?
>
> Best,
> Thomas
>
>
>
Hi Thomas,
You could use *Table* [1]. For instance
Subscript[S, 2] = Table[{m, T[[1,m]] == 2}, {m, 100}]
generates S_2 as an 100 by 2 matrix where the first column ranges from 1
to 100 and the second contains the boolean values True or False
depending on whether the value of T[[1,m]] is equal to 2.
HTH,
Jean-Marc
[1] http://documents.wolfram.com/mathematica/functions/Table