[R] replace an expression with its value, or read macros

From: Franklin Tamborello II <Franklin.Tamborello_at_uth.tmc.edu>
Date: Thu, 07 Apr 2011 23:45:53 +0000


I know my subject line seems odd, but I want to replace an expression—such as a variable—with its value. For example, I want to paste() some strings together, assign the result to a variable s, then use the value of s as a variable to hold another value. Something like this:

import_subjects <- function (start, iterations) { for (i in 1:iterations) { # iterate from start to end s <- paste("s", i, sep="") # make the data.frame's name fn <- paste(i, ".txt", sep="") # make the filename s <- read.delim(fn, header = FALSE) # now put it all together # …except that I don't want to reassign s, I want to evaluate it and make its value a variable with its own value.
}
}

If this were Lisp I'd use backquotes (or "backticks", as some say) and commas—examples of read macros—to do this, but I can't find anything analogous for R. How might I accomplish this in R?

Sincerely,

Frank Tamborello, PhD
W. M. Keck Postdoctoral Fellow
School of Biomedical Informatics
University of Texas Health Science Center at Houston

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