[R] Create function from string

[Jon Olav Skoien]

Thanks a lot, that seems to do exactly what I need!

Best wishes,
Jon

On 16-Apr-13 10:21, peter dalgaard wrote:
> 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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-- 
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.