[R] Question on substitute.

[Uwe Ligges]

Simon Knapp wrote:
> I have a data frame of around 4500 rows which contain file name
> prefixes and other interesting variables. each prefix corresponds to
> multiple files and a I only have 4300 complete sets of files. If any
> one of the files is missing for a given prefix, then the function I
> use fails. The effect is emulated by the function "f" and data
> "dummy.data":
> 
> f <- function(x) if(runif(1) < 0.1) stop('oops') else rnorm(10)
> dummy.data <- data.frame(cbind(paste('a', 1:100, sep=''),
> matrix(rnorm(9000),nrow=100, ncol=9)))
> 
> I would like the results as a data.frame and if it weren't for the
> errors would do:
> 
> res <- apply(dummy.data, 1, function(x) try(f(x))) #... though I
> wouldn't really need the try would I.
> #dimnames(res)[[2]] <- as.character(dummy.data[,1])


So continue with, e.g.:

  valid <- !sapply(res, inherits, "try-error")
  res <- res[valid]
  res <- matrix(unlist(res), ncol=length(res))
  colnames(res) <- as.character(dummy.data[valid,1])

I would not try any of your further questions, they result into slower 
and more unreadable code.

Uwe Ligges



> but the errors make res a list and the second line fails. I can do:
> 
> res <- NULL
> for(i in 1:nrow(dummy.data)) if(class(tmp <- try(f(dummy.data[i,])))
> != 'try-error') res <- cbind(res, tmp)
> 
> which gives me the correct result, but I don't know which column of
> res belongs to which row of dummy.data.
> 
> I can get the desired result with with:
> 
> #--- desired result --------
> res <- NULL
> for(i in 1:nrow(dummy.data)) if(class(tmp <- try(f(dummy.data[i,])))
> != 'try-error')
>     eval(parse(text=paste("res <- cbind(res,", dummy.data[i,1],
> "=tmp)", sep='')))
> #------------------------------
> 
> but it is sort of ugly and I was hoping I could do something like:
> 
> res <- NULL
> for(i in 1:nrow(dummy.data)) if(class(tmp <- try(f(dummy.data[i,])))
> != 'try-error')
>     res <- eval(substitute(cbind(res, a=b), list(a=dummy.data[i,1], b=tmp)))
> 
> but the a is not being substituted (not that this is prettier, but I'm
> trying to come to grips with
> substitute/do.call/calls/expressions/...). I guess that argument names
> are a different beast to argument values in expressions.
> 
> 
> 
> My question (finally) is: is there a way of achieving 'desired
> result', but using 'quote', 'substitute' or any other similar
> functions/idioms I've not run into yet? Alternatively, is there a
> completely different way?
> 
> Any help appreciated,
> Simon Knapp.
> 
> ______________________________________________
> 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.