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
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