R help - Feb 2007 - Extract NULL column in a matrix e.g. matrix[,-NULL]

Hello,

 

I need to remove columns in a matrix.  The number of columns varies from 0
to n.  I can't figure out how to specify the zero case.

 

aa <-matrix(runif(5^2),5,5)

 

#remove column 3

aa[,-3]

 

#remove no column

aa[,-NULL]

Error in -NULL : invalid argument to unary operator

 

I know I could use ifelse, but it would complicate my model a lot. Is there
a direct way to specify that the number of columns to remove is 0?

 

Pierre Lapointe


	[[alternative HTML version deleted]]

Le 07-02-11 ? 11:42, Pierre Lapointe a ?crit :
> Hello,
>
> I need to remove columns in a matrix.  The number of columns varies  
> from 0
> to n.  I can't figure out how to specify the zero case.
>
> aa <-matrix(runif(5^2),5,5)
>
> #remove column 3
>
> aa[,-3]
>
> #remove no column
>
> aa[,-NULL]
>
> Error in -NULL : invalid argument to unary operator
>
> I know I could use ifelse, but it would complicate my model a lot.  
> Is there
> a direct way to specify that the number of columns to remove is 0?
>
> Pierre Lapointe
Would

aa <- if (n > 0) aa[, -n] else aa

still be too complicated?

---
   Vincent Goulet, Associate Professor
   ?cole d'actuariat
   Universit? Laval, Qu?bec
   Vincent.Goulet at act.ulaval.ca   http://vgoulet.act.ulaval.ca

Try:

aa[, !seq(ncol(aa)) %in% NULL]

On 2/11/07, Pierre Lapointe <pierrelap at gmail.com>
wrote:
> Hello,
>
>
>
> I need to remove columns in a matrix.  The number of columns varies from 0
> to n.  I can't figure out how to specify the zero case.
>
>
>
> aa <-matrix(runif(5^2),5,5)
>
>
>
> #remove column 3
>
> aa[,-3]
>
>
>
> #remove no column
>
> aa[,-NULL]
>
> Error in -NULL : invalid argument to unary operator
>
>
>
> I know I could use ifelse, but it would complicate my model a lot. Is there
> a direct way to specify that the number of columns to remove is 0?
>
>
>
> Pierre Lapointe
>
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at stat.math.ethz.ch 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.
>