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 > -- > ------------------------------------------------------------------- > | Olivier Georg \__ e-mail: Olivier.Georg at studi.epfl.ch | > | Rte de Chailly 159 \__ home: http://diwww.epfl.ch/~ogeorg | > | 1814 La Tour-de-Peilz \__ tel: +41 21 944 15 42 | > ------------------------------\__---------------------------------- > | On ne peut pas tuer le temps \__ | > | Sans blesser un peu l'eternite \__ ________ __o | > | ( As if you could kill time ) \__ _____ _`\<,_ | > | ( without injuring eternity. ) \__ ___ (_)/ (_) | > | Henry David Thoreau \ | > ------------------------------------------------------------------- > > 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