[R] avoiding eval parse with indexing

[arun]

Hi,
You could use:
library(abind)
#using Berend's and Bert's example
x1 <- array(runif(9),dim=c(3,3))
x2 <- array(runif(8),dim=c(2,2,2))
z <- array(1:24,dim=2:4)
#applying your code:
 eval(parse(text=paste0("x1[1",paste(rep(",",length(dim(x1))-1),collapse=""),"]")))
#[1] 0.6439062 0.7139397 0.6017418
eval(parse(text=paste0("x2[1",paste(rep(",",length(dim(x2))-1),collapse=""),"]")))
#            [,1]      [,2]
#[1,] 0.026671344 0.2116831
#[2,] 0.003903368 0.1551140
eval(parse(text=paste0("z[1",paste(rep(",",length(dim(z))-1),collapse=""),"]")))
#     [,1] [,2] [,3] [,4]
#[1,]    1    7   13   19
#[2,]    3    9   15   21
#[3,]    5   11   17   23

 asub(x1,1,1,drop=TRUE)
#[1] 0.6439062 0.7139397 0.6017418
 asub(x2,1,1,drop=TRUE)
#            [,1]      [,2]
#[1,] 0.026671344 0.2116831
#[2,] 0.003903368 0.1551140
 asub(z,1,1,drop=TRUE)
#     [,1] [,2] [,3] [,4]
#[1,]    1    7   13   19
#[2,]    3    9   15   21
#[3,]    5   11   17   23
A.K. 



----- Original Message -----
From: Martin Ivanov <tramni at abv.bg>
To: r-help at r-project.org
Cc: 
Sent: Sunday, May 26, 2013 9:56 AM
Subject: [R] avoiding eval parse with indexing

Hello,
I would like to get an advice on how the notorious eval(parse()) construct could possibly 
be avoided in the following example. I have an array x, which can have different number of dimensions,
but I am only interested in extracting, say, the first element of the first dimension. Currently I achieve this
in this way:

eval(parse(text=paste0("x[1", paste(rep(", ", length(dim(x)) - 1), collapse=""), "]")))

Is it possible to avoid the eval parse here? How?

Best regards,

Martin

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