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