R devel - Nov 2005 - x[1,], x[1,,], x[1,,,], ...

Hi,

is there a function in R already doing what I try to do below:

# Let 'x' be an array with *any* number of dimensions (>=1).
x <- array(1:24, dim=c(2,2,3,2))
...
x <- array(1:24, dim=c(4,3,2))

i <- 2:3

ndim <- length(dim(x))
if (ndim == 1)
   y <- x[i]
else if (ndim == 2)
   y <- x[i,]
else if (ndim == 3)
   y <- x[i,,]
else ...

and so on.  My current solution is

ndim <- length(dim(x))
args <- rep(",", ndim)
args[1] <- "i"
args <- paste(args, collapse="")
code <- paste("x[", args, "]", sep="")
expr <- parse(text=code)
y <- eval(expr)

ndim <- length(dim(x))
args <- rep(",", ndim)
args[1] <- "i"
args <- paste(args, collapse="")
code <- paste("x[", args, "]", sep="")
expr <- parse(text=code)
y <- eval(expr)

Is there another way I can do this in R that I have overlooked?

/Henrik

You can look at the definition of 'corner' in the public
domain area of the Burns Statistics website.  It uses
'do.call' on '[' to achieve (sort of) what you want.

Patrick Burns
patrick at burns-stat.com
+44 (0)20 8525 0696
http://www.burns-stat.com
(home of S Poetry and "A Guide for the Unwilling S User")

Henrik Bengtsson wrote:
>Hi,
>
>is there a function in R already doing what I try to do below:
>
># Let 'x' be an array with *any* number of dimensions (>=1).
>x <- array(1:24, dim=c(2,2,3,2))
>...
>x <- array(1:24, dim=c(4,3,2))
>
>i <- 2:3
>
>ndim <- length(dim(x))
>if (ndim == 1)
>   y <- x[i]
>else if (ndim == 2)
>   y <- x[i,]
>else if (ndim == 3)
>   y <- x[i,,]
>else ...
>
>and so on.  My current solution is
>
>ndim <- length(dim(x))
>args <- rep(",", ndim)
>args[1] <- "i"
>args <- paste(args, collapse="")
>code <- paste("x[", args, "]", sep="")
>expr <- parse(text=code)
>y <- eval(expr)
>
>ndim <- length(dim(x))
>args <- rep(",", ndim)
>args[1] <- "i"
>args <- paste(args, collapse="")
>code <- paste("x[", args, "]", sep="")
>expr <- parse(text=code)
>y <- eval(expr)
>
>Is there another way I can do this in R that I have overlooked?
>
>/Henrik
>
>______________________________________________
>R-devel at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-devel
>
>
>
>  
>

Henrik Bengtsson <hb at maths.lth.se> writes:
> Hi,
> 
> is there a function in R already doing what I try to do below:
> 
> # Let 'x' be an array with *any* number of dimensions (>=1).
> x <- array(1:24, dim=c(2,2,3,2))
> ...
> x <- array(1:24, dim=c(4,3,2))
> 
> i <- 2:3
> 
> ndim <- length(dim(x))
> if (ndim == 1)
>    y <- x[i]
> else if (ndim == 2)
>    y <- x[i,]
> else if (ndim == 3)
>    y <- x[i,,]
> else ...
> 
> and so on.  My current solution is
> 
> ndim <- length(dim(x))
> args <- rep(",", ndim)
> args[1] <- "i"
> args <- paste(args, collapse="")
> code <- paste("x[", args, "]", sep="")
> expr <- parse(text=code)
> y <- eval(expr)
> 
> ndim <- length(dim(x))
> args <- rep(",", ndim)
> args[1] <- "i"
> args <- paste(args, collapse="")
> code <- paste("x[", args, "]", sep="")
> expr <- parse(text=code)
> y <- eval(expr)
> 
> Is there another way I can do this in R that I have overlooked?
I think this should work:

x <- array(1:24, dim=c(3,2,2,2)) # not c(2,2,3,2)....
i <- 2:3
ndim <- length(dim(x))
ix <- as.list(rep(TRUE, ndim))
ix[[1]] <- i
do.call("[", c(list(x), ix))


-- 
   O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907

I suppose one can make use of slice.index():
> array(x[slice.index(x, 1) == 1], dim(x)[-1])
     [,1] [,2]
[1,]    1   13
[2,]    5   17
[3,]    9   21

Andy

> From: Henrik Bengtsson
> 
> Hi,
> 
> is there a function in R already doing what I try to do below:
> 
> # Let 'x' be an array with *any* number of dimensions (>=1).
> x <- array(1:24, dim=c(2,2,3,2))
> ...
> x <- array(1:24, dim=c(4,3,2))
> 
> i <- 2:3
> 
> ndim <- length(dim(x))
> if (ndim == 1)
>    y <- x[i]
> else if (ndim == 2)
>    y <- x[i,]
> else if (ndim == 3)
>    y <- x[i,,]
> else ...
> 
> and so on.  My current solution is
> 
> ndim <- length(dim(x))
> args <- rep(",", ndim)
> args[1] <- "i"
> args <- paste(args, collapse="")
> code <- paste("x[", args, "]", sep="")
> expr <- parse(text=code)
> y <- eval(expr)
> 
> ndim <- length(dim(x))
> args <- rep(",", ndim)
> args[1] <- "i"
> args <- paste(args, collapse="")
> code <- paste("x[", args, "]", sep="")
> expr <- parse(text=code)
> y <- eval(expr)
> 
> Is there another way I can do this in R that I have overlooked?
> 
> /Henrik
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
> 
>

Hi everyone


apltake(x,1)

[where apltake() is part of library(magic)]

does this.

best wishes

Robin




On 23 Nov 2005, at 10:50, Henrik Bengtsson wrote:
> Hi,
>
> is there a function in R already doing what I try to do below:
>
> # Let 'x' be an array with *any* number of dimensions (>=1).
> x <- array(1:24, dim=c(2,2,3,2))
> ...
> x <- array(1:24, dim=c(4,3,2))
>
> i <- 2:3
>
> ndim <- length(dim(x))
> if (ndim == 1)
>    y <- x[i]
> else if (ndim == 2)
>    y <- x[i,]
> else if (ndim == 3)
>    y <- x[i,,]
> else ...
>
> and so on.  My current solution is
>
> ndim <- length(dim(x))
> args <- rep(",", ndim)
> args[1] <- "i"
> args <- paste(args, collapse="")
> code <- paste("x[", args, "]", sep="")
> expr <- parse(text=code)
> y <- eval(expr)
>
> ndim <- length(dim(x))
> args <- rep(",", ndim)
> args[1] <- "i"
> args <- paste(args, collapse="")
> code <- paste("x[", args, "]", sep="")
> expr <- parse(text=code)
> y <- eval(expr)
>
> Is there another way I can do this in R that I have overlooked?
>
> /Henrik
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
--
Robin Hankin
Uncertainty Analyst
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743