Re: reading different locations of a matrix specified

*To*: mathgroup at smc.vnet.net*Subject*: [mg113872] Re: reading different locations of a matrix specified*From*: "Nasser M. Abbasi" <nma at 12000.org>*Date*: Tue, 16 Nov 2010 06:14:15 -0500 (EST)

On 11/16/2010 2:30 AM, Oliver Ruebenkoenig wrote: >> ------------------------------------ >> A={{1,2,3},{4,5,6},{7,8,9}}; >> pos={{1,1},{3,3}}; >> >> A[[ ##& @@ #]]& /@ pos >> --------------------------- >> >> {1,9} >> > > Extract[A, pos] > I thought I should add something more as to why I ended up with the command A[[ Sequence @@ #]]& /@ pos It started like this: pos={1,1} Typing A[[ pos ]] does not work as I wanted (to get element A[[ 1,1 ]]) And this what started the whole investigation. I needed a way to remove the '{ }' from around the {1,1} so it will be A[[ 1,1 ]] Then I remembered Sequence does that, so I typed A[[Sequence@@pos]] and that is how I got to the command above. Now, I see that Extract[A,pos] to be equivalent to A[[ Sequence@@pos ]] without the need to have to worry about '{ }' there. So, basically Extract[A,{1,1}] works as meant to be, but A[[ {1,1} ]] did not. So, my choice will be now to use Extract[A,pos] so many commands, so little time :) --Nasser