I said the force was 'required' in the sense that without it the function will fail to do what you want in some situations. It doesn't make sense to write a function that you know will fail sometimes when you know an easy way to make it work in all situations.
Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com From: Mark Leeds [mailto:marklee...@gmail.com] Sent: Thursday, June 06, 2013 8:57 AM To: William Dunlap Cc: Liviu Andronic; r-help@r-project.org Help Subject: Re: [R] generate simple function with pre-defined constants hi bill: I understand what you're doing but, atleast for this case, I checked and you don't need the force this one. it works without it. so, I think the force requirement applies only when you're building them up with the lapply. but definitely I'm opened to clarification. thanks. On Thu, Jun 6, 2013 at 11:36 AM, William Dunlap <wdun...@tibco.com<mailto:wdun...@tibco.com>> wrote: Try the following: generateABFunction <- function(a, b) { force(a) force(b) function(x) a*x + b } f12 <- generateABFunction(1, 2) f53 <- generateABFunction(5,6) f12(10:12) # get 12, 13, 14 f53(10:12) # get 56, 61, 66 See, e.g., yesterday's discussion under the subject "Trying to build up functions with its names by means of lapply" on why the force() calls are required. Read up on R's environments to see why f12 and f53 look the same but act differently (hint: look at ls.str(environment(f12))). Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com<http://tibco.com> > -----Original Message----- > From: r-help-boun...@r-project.org<mailto:r-help-boun...@r-project.org> > [mailto:r-help-boun...@r-project.org<mailto:r-help-boun...@r-project.org>] On > Behalf > Of Liviu Andronic > Sent: Thursday, June 06, 2013 8:00 AM > To: r-help@r-project.org<mailto:r-help@r-project.org> Help > Subject: Re: [R] generate simple function with pre-defined constants > > On Thu, Jun 6, 2013 at 4:48 PM, Liviu Andronic > <landronim...@gmail.com<mailto:landronim...@gmail.com>> wrote: > > Dear all, > > Given: > > a <- 2 > > b <- 3 > > > > I'd like to obtain the following function: > > f <- function(x) 2 + 3*x > > > > but when I do this: > > f <- function(x) a + b*x > > ##f > > ##function(x) a + b*x > > > > the 'a' and 'b' objects do not get evaluated to their constants. How > > could I do that? > > > I found one solution: > a <- 2 > b <- 3 > f <- eval(parse(text=paste("function(z)", a, "+ z * ", b))) > f > ##function(z) 2 + z * 3 > > but I still have nightmares from: > > fortune("parse") > > If the answer is parse() you should usually rethink the question. > -- Thomas Lumley > R-help (February 2005) > > Is there a nicer way to approach this? Thanks, > Liviu > > > > Thanks, > > Liviu > > > > > > -- > > Do you know how to read? > > http://www.alienetworks.com/srtest.cfm > > http://goodies.xfce.org/projects/applications/xfce4-dict#speed-reader > > Do you know how to write? > > http://garbl.home.comcast.net/~garbl/stylemanual/e.htm#e-mail > > > > -- > Do you know how to read? > http://www.alienetworks.com/srtest.cfm > http://goodies.xfce.org/projects/applications/xfce4-dict#speed-reader > Do you know how to write? > http://garbl.home.comcast.net/~garbl/stylemanual/e.htm#e-mail > > ______________________________________________ > R-help@r-project.org<mailto: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. ______________________________________________ R-help@r-project.org<mailto: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.
