Re: extracting elements from a list of lists
- To: mathgroup at smc.vnet.net
- Subject: [mg5834] Re: [mg5811] extracting elements from a list of lists
- From: Francisco Edmundo de Andrade <edmundo at lia.ufc.br>
- Date: Tue, 28 Jan 1997 03:42:58 -0500
- Sender: owner-wri-mathgroup at wolfram.com
On Wed, 22 Jan 1997, Olivier Georg wrote:
> Hi,
>
> Suppose I have lists within a list, like:
>
> myList = {{a,b}, {c,d}}
>
> and I want to extract some element (let's say the d).
> I can request:
>
> myList[[2,2]].
>
> Now suppose what I have the index of the element as
> the list {2,2}. Then I can do:
>
> Fold[Part, myList, {2,2}]
>
> Is it correct to suppose that it will first return the
> 2nd sublist, and then extract the second element from it?
> How efficient is it? This may be a crucial point
> if I have long lists, I think. Then isn't there a
> better way of doing this?
>
> Olivier
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>
>
Dear Olivier,
I think the follow solution is faster than Fold[Part, myList, {2,2}]:
myList[[Sequence @@ {2,2}]]
once that the application of indexes is direct!
With best wishes,
EDMUNDO
(Edmundo's contribuitions 1997)
Universidade Federal do Ceara
Fortaleza - CE - Brasil
Departamento de Computacao