R help - Nov 2008 - what is there in a numeric (0)?

Hello!
 I will repeat my question :what is there in a numeric(0)?

 In a function, I have several matrices with dimensions 288x1, also matrices
with dimensions
 0x1 (numeric(0)).
 But I really do not know in which matrix there are elements or not.
 So, these matrices that do not contain anything, if I am saying this correctly,
I would like to make them
 matrices with the same dimensions as the first ones but with NA elements and
the ones with elements to remain as they
 are.
 For this reason, I thought to use the ifelse command. But I have problems
determining the arguments of this ifelse...
 I tried to use: 
 A1 <- ifelse(nrow(A)==0,matrix(rep(NA,288),288,1),A)

 If A is a matrix with elements, then I get a A1 matrix with replicated 288
times its first element, but I want the
 initial A matrix. If A is a matrix with no elements (numeric(0)) then I get
only 1 NA.
 
So, how can I test if there are elements in my matrix and if there are to return
itself the matrix and if there are not to get a matrix 288x1 with NAs?
Thank you for your time!

Ismini

Hi

r-help-bounces at r-project.org napsal dne 27.11.2008 11:48:32:
> 
>  Hello!
>  I will repeat my question :what is there in a numeric(0)?
> 
>  In a function, I have several matrices with dimensions 288x1, also 
matrices 
> with dimensions 
>  0x1 (numeric(0)).
>  But I really do not know in which matrix there are elements or not.
>  So, these matrices that do not contain anything, if I am saying this 
> correctly, I would like to make them
>  matrices with the same dimensions as the first ones but with NA 
elements and 
> the ones with elements to remain as they 
>  are.
>  For this reason, I thought to use the ifelse command. But I have 
problems 
> determining the arguments of this ifelse...
>  I tried to use: 
>  A1 <- ifelse(nrow(A)==0,matrix(rep(NA,288),288,1),A)
> 
>  If A is a matrix with elements, then I get a A1 matrix with replicated 
288 
> times its first element, but I want the 
>  initial A matrix. If A is a matrix with no elements (numeric(0)) then I 
get 
> only 1 NA. 
It is not a work for ifelse but for if. You want to test only one 
comparison not a vector of values.

if(nrow(mat)==0) A1 <- matrix(NA, 288,1) else A1 <- A

Regards
Petr

> 
> So, how can I test if there are elements in my matrix and if there are 
to 
> return itself the matrix and if there are not to get a matrix 288x1 with 
NAs?
> Thank you for your time!
> 
> Ismini
> 
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