How to read in a vector stored as a R expression in a text file (and other things)

A Facebook friend asked:

R question: I have a file that contains a list of entries of the format "c(2.34306542445513, 1.07370083005978e-06)". How can I coax R to read such entries literally? In other words, I want to make an object from the entries. pars <- c(2.34306542445513, 1.07370083005978e-06)

My first response was to do this the hard way. Let's say we have a text file with one or multiple rows as described:

c(2.34306542445513, 1.07370083005978e-06) c(0.71697056549601, 0.03731942130253) c(1.29112553643060, 1.41375523433091) c(0.1173946523107, 0.14024055395275)

Before realizing that there is a much easier way, I pointed out that we can do what's been proposed using readLines, strsplit, paste, and as.numeric. I include this primarily to emphasize how easy it :

> y<-readLines("datafile.txt",4) > x<-strsplit(y,"") > x<-lapply(x,function(x) paste(x[3:(length(x)-1)], collapse="")) > x<-lapply(x,function(x) strsplit(x,", ")[[1]]) > X<-sapply(x,as.numeric) > X [,1] [,2] [,3] [,4] [1,] 2.343065e+00 0.71697057 1.291126 0.1173947 [2,] 1.073701e-06 0.03731942 1.413755 0.1402406

Anyway, shortly after posting this I realized that this could be done much more easily using the functions eval and parse:

> y<-readLines("datafile.txt",4) > X<-apply(as.matrix(y),1,function(x) eval(parse(text=x))) > X [,1] [,2] [,3] [,4] [1,] 2.343065e+00 0.71697057 1.291126 0.1173947 [2,] 1.073701e-06 0.03731942 1.413755 0.1402406

That's it!

P.S. please let me know if you prefer this new "text box" format for R code and session results, or my previous method of font only based demarcation (e.g., shown here, and in almost any other post on this blog).