[R] avoiding eval parse with indexing

[arun]

Hi,
Another way would be:
library(arrayhelpers)
 slice(aperm(x1,c(2,1)),j=1)
#[1] 0.6439062 0.7139397 0.6017418
 slice(aperm(x2,c(2,1,3)),j=1)
#            [,1]      [,2]
#[1,] 0.026671344 0.2116831
#[2,] 0.003903368 0.1551140


  slice(aperm(z,c(2,1,3)),j=1)
#     [,1] [,2] [,3] [,4]
#[1,]    1    7   13   19
#[2,]    3    9   15   21
#[3,]    5   11   17   23

#or
  array(z[slice.index(z,1)==1],dim= dim(z)[2:3])
#     [,1] [,2] [,3] [,4]
#[1,]    1    7   13   19
#[2,]    3    9   15   21
#[3,]    5   11   17   23
array(x2[slice.index(x2,1)==1],dim= dim(x2)[2:3])
#            [,1]      [,2]
#[1,] 0.026671344 0.2116831
#[2,] 0.003903368 0.1551140
array(x1[slice.index(x1,1)==1],dim= dim(x1)[1])
#[1] 0.6439062 0.7139397 0.6017418
A.K.

 



----- Original Message -----
From: arun <smartpink111 at yahoo.com>
To: Martin Ivanov <tramni at abv.bg>
Cc: R help <r-help at r-project.org>; Berend Hasselman <bhh at xs4all.nl>; Bert Gunter <gunter.berton at gene.com>
Sent: Sunday, May 26, 2013 11:48 AM
Subject: Re: [R] avoiding eval parse with indexing

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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