RE: extracting elements from an expression
- To: mathgroup at smc.vnet.net
- Subject: [mg27689] RE: [mg27663] extracting elements from an expression
- From: "Harvey P. Dale" <hpd1 at nyu.edu>
- Date: Sun, 11 Mar 2001 04:04:31 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
Albert: How about Union[Flatten[m]]? Best, Harvey Professor Harvey P. Dale New York University School of Law Room 206A 110 West 3rd Street New York, N.Y. 10012-1074 -----Original Message----- From: Albert Maydeu-Olivares [mailto:amaydeu at tinet.fut.es] To: mathgroup at smc.vnet.net Sent: Saturday, March 10, 2001 12:50 AM To: mathgroup at smc.vnet.net Subject: [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