Thanks. It's a great solution to part of my problem. It provides the functionally I want would be no harder for students to use than my approach. I'm still interested in how to make what I was trying to do work -- simply to add to my own R programming proficiency. Joel
________________________________ From: Erik Iverson [mailto:eiver...@nmdp.org] Sent: Thu 8/13/2009 4:59 PM To: Pitt, Joel; r-help@r-project.org Subject: RE: Coding problem: How can I extract substring of function callwithin the function Are you sure you just don't want to tell them about the :: operator? It sounds easier than what you're proposing. E.g., base::mean(c(1:10, NA)) -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Pitt, Joel Sent: Thursday, August 13, 2009 3:48 PM To: r-help@r-project.org Subject: [R] Coding problem: How can I extract substring of function call within the function In order to ease my students into the R environment I am developing a package which installs a variety of utility functions as well as slightly modified versions of some standard R functions -- e.g. mean, hist, barplot, .... In my versions of these standard R functions I either add options or alter some defaults that seem to create difficulties for most of my students -- for example, when they do barcharts for two dimensional tables they generally want the bars to be side-by-side and stumble over the standard default of besides=F, and my version of mean by default reports a mean value in the presence of NA's after warning of that presence (but retains the option of setting na.rm=F). (I don't doubt that some (if not many) of you will doubt the wisdom of this, and I would be happy to discuss this in more detail on other occasions.) You might want to think of my replacement R functions as a kind of "training wheels" for R, and, in the spirit of training wheels I include a funct! ion in my package that allows a user to revert to the standard version of one or all functions without unloading the package (and loosing its additional functionality). However, I want to add a function that allows a user to revert to running the standard R version of a given function on a one-off basis and that's where my problem comes up. I believe that it should be possible to write a function rStd with the usage rStd(x,...) where x is a function -- e.g. mean, hist, barchart, and the remaining parameters would be any of the parameters that should be passed to the unmodified version of mean, hist, barchart... The problem I have is how to get ahold of that collection of parameters as a single character string. Now I know that sys.calls()[[1]] will give me the full text of the initial call, but the problem is to detach the ... above from that as a text string. If I could do that I'd be done. Here's the incomplete code with comments -- see the gap set off by astericks. rStd=function(x,...){ if(missing(x)) # must have a specified function { cat("Error: No function specified\n"); return(invisible(NULL)); } z=as.character(substitute(x)); # must include code here to check that z is the name # of one of our altered functions # if z is an altered function, e.g., "mean" # then concatenating "x" with z gives the overlaid # function -- e.g. xmean is the standard mean #*************************************************************************** # Now we need to get a hold of the ... text * # * w=sys.calls()[[1]]; # this gets me the whole text of the call * # * # and now here's where the problem arises * # how to I get the ... text if I could get it and say * # assign it to the variable params * # I could then set * # * cmd=sprintf("x%s(%s)",z,params) # see remarks above about z # and then it's done.... eval(parse(text=cmd),sys.frame()); } Any help would be much appreciated. Regards Joel Joel Pitt, Ph.D. Associate Professor & Chair Mathematics & Computer Science Georgian Court University 900 Lakewood Avenue Lakewood, NJ 08540 732-987-2322 [[alternative HTML version deleted]] ______________________________________________ R-help@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. [[alternative HTML version deleted]] ______________________________________________ R-help@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.
