[R] avoiding eval parse with indexing

[Martin Ivanov]

Dear Arun,

Thank You very much, your suggestion also works and seems to also be more convenient.
I think though, that Mr Gunter's suggestion should be more efficient, as it uses directly the Extract operator.

Thank You all very much for Your responsiveness. R does have a wonderful community!

Best regards,
Martin



 >-------- Оригинално писмо --------
 >От:  arun 
 >Относно: Re: [R] avoiding eval parse with indexing
 >До: Martin Ivanov 
 >Изпратено на: Неделя, 2013, Май 26 18:48:33 EEST
 >
 >
 >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 
 >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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 >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.
 >
 >