Re: Clever way to manipulate lists
- To: mathgroup at smc.vnet.net
- Subject: [mg94398] Re: [mg94366] Clever way to manipulate lists
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Thu, 11 Dec 2008 07:31:20 -0500 (EST)
- Reply-to: hanlonr at cox.net
list1 = {{x1, y1}, {x2, y2}, {x3, y3}, {xN, yN}}; list2 = {{x1, z1}, {x3, z3}, {xN, zN}}; Select[list1, MemberQ[list2[[All, 1]], #[[1]]] &] {{x1, y1}, {x3, y3}, {xN, yN}} Cases[list1, _?(MemberQ[list2[[All, 1]], #[[1]]] &)] {{x1, y1}, {x3, y3}, {xN, yN}} DeleteCases[list1, _?(FreeQ[list2[[All, 1]], #[[1]]] &)] {{x1, y1}, {x3, y3}, {xN, yN}} Bob Hanlon ---- guerom00 <guerom00 at gmail.com> wrote: ============= Hi everyone, I'm still struggling through lists manipulation. I'll take a concrete example to illustrate my point. Let's say I have a first list, say coordinates on a regular grid : list1={{x1,y1},{x2,y2},{x3,y3}...{xN,yN}} This obviously has a Length of N. Now, let's say I have a second list. In this one, there are fewer than N elements, some points are missing... Let's say it misses a point at x2 : list2 ={{x1,z1},{x3,z3},{x4,z4}...{xN,zN}} Now, since those two lists are not of the same length, I cannot add them, substract them or something. But list2 is included in list1 (in the sense of set theory). Now, what I want to do is, in this example, remove the point {x2,y2} from list1 and then the two list will have the same length and I'll be able to manipulate them as I want. Right now, I do that with For loops (detect elements which are in list1 and not in list2 and delete them, etc...) and that works but it is not elegant. I'm looking for a concise, elegant way to do that if somebody sees what I mean... Thanks in advance :) -- Bob Hanlon