Re: How can this MapAt application be done more efficiently

*To*: mathgroup at smc.vnet.net*Subject*: [mg4219] Re: [mg4180] How can this MapAt application be done more efficiently*From*: Allan Hayes <hay at haystack.demon.co.uk>*Date*: Tue, 18 Jun 1996 03:26:30 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Joel Cannon <cannon at alpha.centenary.edu> [mg4180] How can this MapAt application be done more efficiently wants to drop the zeros form an expression like lst = {{5, 0}, {4, 1}, {3, 2, 0}, {3, 1, 1}} Joel: DeleteCases[#,0]&/@lst {{5}, {4, 1}, {3, 2}, {3, 1, 1}} You add > >Here is my function, with another function that it calls: > dropzero[a_] := > MapAt[droplast,a, Partition[ Map[First,Position[a,0]],1] ] > droplast[a_] := Drop[a, -1] > >It feels to me like two things could be improved. > >1. I had to define the function droplast because I couldn't figure >out >how to use Drop[#,-1] with in the MapAt expression and get it to >work. > >2. Of less importance, >the argument "Partition[Map[First,Position[a,0]],1]" seems a bit >clumsy. Pure functions are very useful. Re 1. : MapAt[Drop[#,-1]&,a, Partition[ Map[First,Position[a,0]],1] ] Re 2: MapAt[Drop[#,-1]&,a, Position[lst,_?(MemberQ[#,0]&)] ] Allan Hayes hay at haystack.demon.co.uk 12-06-96 ==== [MESSAGE SEPARATOR] ====