[R] Create function from string

[peter dalgaard]

Is this what you are looking for?

> FUN = eval(bquote(function(x) .(parse(text = fstring)[[1]])))
> FUN
function (x) 
x + 2
> FUN(3)
[1] 5



On Apr 16, 2013, at 09:50 , Jon Olav Skoien wrote:

> Dear list,
> 
> I am trying to create a function from a string, and have so far solved it with eval(parse()). This works well also when using the newly created function as an argument to another function. The trouble starts when I want to use it with parLapply. Below is a much simplified example:
> 
> ##############
> fstring = "x+2"
> FUN = function(x)  eval(parse(text = fstring))
> FUN(3)
> 
> FUN2 = function(y, func)   y + func(y)
> FUN2(3,FUN)
> 
> # I can also pass FUN as an argument to FUN2 when using foreach and parallel:
> 
> library(parallel)
> library(foreach)
> cl = makeCluster(2, outfile = "")
> 
> ylist = list(1:3,4:6)
> result = foreach(i = 1:2) %dopar% {
>  FUN2(ylist[[i]], FUN)
> }
> 
> # But now when I wanted to change to parLapply (actually parLapplyLB) fstring is not found anymore:
> parLapply(cl, as.list(1:4), FUN2, func = FUN)
> ##############
> 
> I assume there is a problem with environments, the question is how to solve this. The cleanest would be to substitute fstring with its content in FUN, but I did not figure out how. Substitute or bquote do not seem to do the trick, although I might not have tried them in the right way. Any suggestions how to solve this, either how to substitute correctly, or to completely avoid the eval(parse())?
> 
> Thanks,
> Jon
> 
> 
> 
> -- 
> Jon Olav Skøien
> Joint Research Centre - European Commission
> Institute for Environment and Sustainability (IES)
> Land Resource Management Unit
> 
> Via Fermi 2749, TP 440,  I-21027 Ispra (VA), ITALY
> 
> jon.skoien at jrc.ec.europa.eu
> 
> Disclaimer: Views expressed in this email are those of the individual and do not necessarily represent official views of the European Commission.
> 
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-- 
Peter Dalgaard, Professor
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com