R help - Nov 2008 - How to avoid "$ operator is invalid for atomic vectors"

Hi,

I am writing this in a wrong way, can someone please correct me?
> A <- matrix()
> length(A) <- 6
> dim(A) <- c(3,2)
> colnames(A) <- c("X","Y")
> A
      X  Y
[1,] NA NA
[2,] NA NA
[3,] NA NA
> A$X
Error in A$X : $ operator is invalid for atomic vectors
>
Thanks,
cruz

Hello -

cruz wrote:
> Hi,
> 
> I am writing this in a wrong way, can someone please correct me?
> 
>> A <- matrix()
>> length(A) <- 6
>> dim(A) <- c(3,2)
>> colnames(A) <- c("X","Y")
>> A
>       X  Y
> [1,] NA NA
> [2,] NA NA
> [3,] NA NA
>> A$X
> Error in A$X : $ operator is invalid for atomic vectors
A[, "X"] may be what you want?

See the details of ?Extract about how '$' only works on recursive 
(list-like) objects, of which your matrix A is not one of.
> 
> Thanks,
> cruz
> 
> ______________________________________________
> 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.

Hi Cruz
you don't need to assign dimension or classes to your objects.
It's easier if you  do like this

> a=c(0,1,2,4,1,1)
> length(a)
[1] 6
> b=matrix(a,3,2,byrow=T)
> b
     [,1] [,2]
[1,]    0    1
[2,]    2    4
[3,]    1    1
of course you can change the colnames and assign what 
you prefer
> colnames(b)=c("x","y")
but if you try to recall "x" with
b$x 
is not going to work
like that, 
you have two option:

1. switch  form matrix to a dataframe:
> c=as.data.frame(b)
> c
  x y
1 0 1
2 2 4
3 1 1
> c$x
[1] 0 2 1

no problems.

2. Can get the column  "x"
on the matrix b as
b[,1]
[1] 0 2 1

just giving the  position.


Hope that this helps.

Best Regards
Anna



 Anna Freni Sterrantino
Ph.D Student 
Department of Statistics
University of Bologna, Italy
via Belle Arti 41, 40124 BO.




________________________________
Da: cruz <cruadam@gmail.com>
A: r-help@r-project.org
Inviato: Giovedì 6 novembre 2008, 17:22:42
Oggetto: [R] How to avoid "$ operator is invalid for atomic vectors"

Hi,

I am writing this in a wrong way, can someone please correct me?
> A <- matrix()
> length(A) <- 6
> dim(A) <- c(3,2)
> colnames(A) <- c("X","Y")
> A
      X  Y
[1,] NA NA
[2,] NA NA
[3,] NA NA
> A$X
Error in A$X : $ operator is invalid for atomic vectors
>
Thanks,
cruz

______________________________________________
R-help@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.



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