RE: extracting elements from an expression
- To: mathgroup at smc.vnet.net
- Subject: [mg27702] RE: [mg27663] extracting elements from an expression
- From: "tgarza01 at prodigy.net.mx" <tgarza01 at prodigy.net.mx>
- Date: Sun, 11 Mar 2001 04:04:50 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
I'm not sure I understood your question. The following obviously obtains what you seem to be asking for, but it looks quite trivial to me. Perhaps you could clarify: In[1]:= Union[Flatten[m]] Out[1]= {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21} Tomas Garza Mexico City Original Message: ----------------- From: Albert Maydeu-Olivares amaydeu at tinet.fut.es To: mathgroup at smc.vnet.net Subject: [mg27702] [mg27663] extracting elements from an expression Dear all, I've spent several frustrating hours attempting to do something in principle very simple. After repeated failures I'm resorting to the group for help. Consider this simple expression m = {{{{1, 2}, {2, 3}}}, {{{4, 5}, {8, 9}}, {{6, 7}, {7, 10}}}, {{{11, 12}, {17, 18}}, {{13, 14}, {19, 20}}, {{15, 16}, {16, 21}}}}; m // TableForm I'm simply trying to obtain to obtain this list {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21} using the positions' elements in m. This will do it the hard way Join[m[[1, 1, 1]], Drop[m[[1, 1, 2]], 1], m[[2, 1, 1]], m[[2, 2, 1]], m[[2, 1, 2]], Drop[m[[2, 2, 2]], 1], m[[3, 1, 1]], m[[3, 2, 1]], m[[3, 3, 1]], m[[3, 1, 2]], m[[3, 2, 2]], Drop[m[[3, 3, 2]], 1]] I've failed to do it the easy way. Here's one of my failed attemps Table[If[i == j && k == 2, Drop[m[[i, j, k]], 1], m[[i, j, k]]], {i, nvars}, {j, i}, {k, 2}] // Flatten which fails because I don't know how to control the k subscript appropriately as you can see by doing Flatten[Table[{i, j, k}, {i, nvars}, {j, i}, {k, 2}],2] Any help would be very much appreciated. Albert -------------------------------------------------------------------- Mail2Web - Check your email from the web at http://www.mail2web.com/ .