Re: Newbie question: pairswise function application

*To*: mathgroup at smc.vnet.net*Subject*: [mg23865] Re: Newbie question: pairswise function application*From*: "Allan Hayes" <hay at haystack.demon.co.uk>*Date*: Thu, 15 Jun 2000 00:51:05 -0400 (EDT)*References*: <8i1t6n$jn9@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Sidney: pairs[data_] := Transpose[Apply[Join, NestList[#, #[data], Length[data] - 2]] & /@ {Drop[#, -1] &, Drop[#, 1] &}] Is a quick way of getting all the pairs that you need, but not in the order that you gave. prs = pairs[L] {{1, 5}, {5, 19}, {19, 100}, {100, 101}, {1, 19}, {5, 100}, {19, 101}, {1, 100}, {5, 101}, {1, 101}} f @@@ prs {f[1, 5], f[5, 19], f[19, 100], f[100, 101], f[1, 19], f[5, 100], f[19, 101], f[1, 100], f[5, 101], f[1, 101]} If you need the pairs to be ordered then: f @@@ Sort[prs] {f[1, 5], f[1, 19], f[1, 100], f[1, 101], f[5, 19], f[5, 100], f[5, 101], f[19, 100], f[19, 101], f[100, 101]} -- Allan --------------------- Allan Hayes Mathematica Training and Consulting Leicester UK www.haystack.demon.co.uk hay at haystack.demon.co.uk Voice: +44 (0)116 271 4198 Fax: +44 (0)870 164 0565 "Sidney Cadot" <sidney at janis.pds.tudelft.nl> wrote in message news:8i1t6n$jn9 at smc.vnet.net... > Hi, > > Wandering through the 1500-odd pages of the Mathematica book, I can't > find the solution to the following rather silly problem: > > I have a list L consisting of (a lot of) integers, and I want to apply a > function f to all pairs of numbers; furthermore, I don't want to > calculate both f[a,b] and f[b,a]: > > L = {1,5,19,100}; > > ... and I want: > > { f[1,5], f[1,19], f[1,100], f[5,19], f[5,100], f[19,100] } > > Can anyone please tell me how to do this? I'd prefer a smart solution > (i.e., not just generating all pairs, then throwing away a lot of them) > since my lists tend to get rather large. > > Thanks in advance, > > Sidney Cadot > sidney at janis.pds.twi.tudelft.nl >