RE: Newbie question: pairswise function application

*To*: mathgroup at smc.vnet.net*Subject*: [mg23868] RE: [mg23857] Newbie question: pairswise function application*From*: "David Park" <djmp at earthlink.net>*Date*: Thu, 15 Jun 2000 00:51:07 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

> -----Original Message----- > From: Sidney Cadot [mailto:sidney at janis.pds.tudelft.nl] To: mathgroup 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 > Sidney, This is one method: li = {1, 5, 9, 100}; Flatten[Table[f[li[[i]], li[[j]]], {i, 1, Length[li] - 1}, {j, i + 1, Length[li]}]] {f[1, 5], f[1, 9], f[1, 100], f[5, 9], f[5, 100], f[9, 100]} David Park djmp at earthlink.net http://home.earthlink.net/~djmp/