Re: apparently I don't know how to use Map (or Apply or MapThread)

*To*: mathgroup at smc.vnet.net*Subject*: [mg77371] Re: apparently I don't know how to use Map (or Apply or MapThread)*From*: mwjdavidson at googlemail.com*Date*: Thu, 7 Jun 2007 03:58:52 -0400 (EDT)*References*: <f4676i$1n3$1@smc.vnet.net>

On Jun 6, 1:52 pm, dbsearc... at yahoo.com wrote: > I started with this: > > m = {{0.098, 0.951, 0.954}, {0.509, 0.914, 0.487}} > > I tried to do this > > Table[#[[i, i]], {i, Length[#]}] & /@ m > I take it you are trying to extract the diagonal elements from your matrix m ? If so why not use Diagonal[m] which gives you the same result as your function definition. Your example using map does not work because map iterates over 1 row at a time. As each of your rows is a 1 x three elements long list #[[i,i]] cannot exist for i > 1. malcolm > It does not work, but this works > > Diag := Function[x, Table[x[[i, i]], {i, Length[x]}]]; Diag[m] > > !@#$%^&*( > > Can anyone tell me why? I also tried: Apply, MapThread, > DiagonalMatrix, TakeMatrix, adding () around the pure function... > > I know that this is a simple problem. Would Evaluate help? > > TIA. > > Regards..