R help - Mar 2010 - Getting multiple matrix-values using a single command

Dear all!

I'm trying to get multiple values from a matrix by using a single  
command.

Given a matrix A

A <- matrix(seq(1,9),nrow=3,ncol=3)

How can I get e.g. the values A[1,2] = 4 and A[3,3] = 9 with a single  
command and without using any loop? My first idea was to generate a  
row- and a column vector for the indices, i.e. c(1,3) indicating row  
number 1 (for A[1,2]) and row number 3 (for A[3,3]) and similar for  
column-indices. Then I've tried to call

A[c(1,3),c(2,3)]

but instead of 4 , 9 the result is

[,1] [,2]
[1,]    4    7
[2,]    6    9

Any suggestions?

Regards, Nils

use a matrix of n x 2 to index. For details: sec. 5.3 "Index matrices"
in the
introduction.

HTH Claudia

Nils R?fenacht wrote:
> Dear all!
> 
> I'm trying to get multiple values from a matrix by using a single
command.
> 
> Given a matrix A
> 
> A <- matrix(seq(1,9),nrow=3,ncol=3)
> 
> How can I get e.g. the values A[1,2] = 4 and A[3,3] = 9 with a single 
> command and without using any loop? My first idea was to generate a row- 
> and a column vector for the indices, i.e. c(1,3) indicating row number 1 
> (for A[1,2]) and row number 3 (for A[3,3]) and similar for 
> column-indices. Then I've tried to call
> 
> A[c(1,3),c(2,3)]
> 
> but instead of 4 , 9 the result is
> 
> [,1] [,2]
> [1,]    4    7
> [2,]    6    9
> 
> Any suggestions?
> 
> Regards, Nils
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

-- 
Claudia Beleites
Dipartimento dei Materiali e delle Risorse Naturali
Universit? degli Studi di Trieste
Via Alfonso Valerio 6/a
I-34127 Trieste

phone: +39 0 40 5 58-37 68
email: cbeleites at units.it

Try this:

 diag(A[c(1,3),c(2,3)])

2010/3/12 Nils R?fenacht <nils.ruefenacht at
bluewin.ch>:
> Dear all!
>
> I'm trying to get multiple values from a matrix by using a single
command.
>
> Given a matrix A
>
> A <- matrix(seq(1,9),nrow=3,ncol=3)
>
> How can I get e.g. the values A[1,2] = 4 and A[3,3] = 9 with a single
> command and without using any loop? My first idea was to generate a row-
and
> a column vector for the indices, i.e. c(1,3) indicating row number 1 (for
> A[1,2]) and row number 3 (for A[3,3]) and similar for column-indices. Then
> I've tried to call
>
> A[c(1,3),c(2,3)]
>
> but instead of 4 , 9 the result is
>
> [,1] [,2]
> [1,] ? ?4 ? ?7
> [2,] ? ?6 ? ?9
>
> Any suggestions?
>
> Regards, Nils
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paran?-Brasil
25? 25' 40" S 49? 16' 22" O

On Mar 12, 2010, at 9:26 AM, Nils R?fenacht wrote:
> Dear all!
>
> I'm trying to get multiple values from a matrix by using a single  
> command.
>
> Given a matrix A
>
> A <- matrix(seq(1,9),nrow=3,ncol=3)
>
> How can I get e.g. the values A[1,2] = 4 and A[3,3] = 9 with a  
> single command and without using any loop? My first idea was to  
> generate a row- and a column vector for the indices, i.e. c(1,3)  
> indicating row number 1 (for A[1,2]) and row number 3 (for A[3,3])  
> and similar for column-indices. Then I've tried to call
>
> A[c(1,3),c(2,3)]
>
> but instead of 4 , 9 the result is
>
> [,1] [,2]
> [1,]    4    7
> [2,]    6    9
Pass the indices in a matrix:

 >  A[matrix(c(c(1,3), c(2,3)), ncol=2)]
[1] 4 9

-- 
David
>
> Any suggestions?
>
> Regards, Nils
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT

Everyone is being too complicated.

   c( A[1,2] , A[3,3] )

will do what you ask.
>  A <- matrix(seq(1,9),nrow=3)
>  c( A[1,2] , A[3,3] )
[1] 4 9

But I would assume you have some more general 
problem in mind, and I do not know if this simple 
approach will meet those needs.

-Don

At 3:26 PM +0100 3/12/10, Nils R?fenacht wrote:
>Dear all!
>
>I'm trying to get multiple values from a matrix by using a single
command.
>
>Given a matrix A
>
>A <- matrix(seq(1,9),nrow=3,ncol=3)
>
>How can I get e.g. the values A[1,2] = 4 and 
>A[3,3] = 9 with a single command and without 
>using any loop? My first idea was to generate a 
>row- and a column vector for the indices, i.e. 
>c(1,3) indicating row number 1 (for A[1,2]) and 
>row number 3 (for A[3,3]) and similar for 
>column-indices. Then I've tried to call
>
>A[c(1,3),c(2,3)]
>
>but instead of 4 , 9 the result is
>
>[,1] [,2]
>[1,]    4    7
>[2,]    6    9
>
>Any suggestions?
>
>Regards, Nils
>
>______________________________________________
>R-help at r-project.org mailing list
>https://*stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide
http://*www.*R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.

-- 
---------------------------------
Don MacQueen
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
macq at llnl.gov