Re: Extracting elements of lists

*To*: mathgroup at smc.vnet.net*Subject*: [mg45495] Re: Extracting elements of lists*From*: bobhanlon at aol.com (Bob Hanlon)*Date*: Sat, 10 Jan 2004 00:00:41 -0500 (EST)*References*: <btncql$1s$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Here are a few ways: data = Table[Random[], {6},{4}]; extracts1 = data[[All,{1,2}]]; extracts2 = {#[[1]],#[[2]]}& /@ data; extracts3 = Take[#,2]& /@ data; extracts4 = Drop[#,-2]& /@ data; extracts1 == extracts2 == extracts3 == extracts4 True Bob Hanlon In article <btncql$1s$1 at smc.vnet.net>, sashan <nothing at important.com> wrote: << I'm trying to extract a elements from a list and return another list with those elements. I've tried doing it using a while loop and recursion and haven't been able to do it. The list I'm working with is a list of lists where each inner list contains 4 elements. Example: {{0, 1, 0, 0}, {0.04, 1, -0.0008, 0}, {0.1, 0.999987, -0.00499995, 0}, {0.15, 0.999937, -0.0112494, 0}, {0.18, 0.999869, -0.0161983, 0},.... This is my recursive attempt: listoftimex[l_] := {{First[l][[1]], First[l][[2]]}, listoftimex[Rest[l]]} {{0, 1}, {{0.04, 1}, {{0.1, 0.999987}, {{ 0.15, 0.999937}, {{0.18, 0.999869}, {{0.23, 0.99965}, {{0.26, 0.999429}, \ {{0.31, 0.998847}, {{0.35, 0.998128}, {{0.39, It extracts the 1st 2 elements of the list and puts them in a list but it nests lists too deep (too many { ) and it errors with 'Recursion depth of 256 exceeded'. This is my attempt using a while loop: timex[l_] := Module[{i = 1, ans = {}}, While[i < Length[l], Append[ans, {l[[i, 1]], l[[i, 2]]}]; i = i + 1]; Return[ans]]; This doesn't work and returns an empty list {}. >><BR><BR>