[R] Evaluating an expression
David Winsemius
dwinsemius at comcast.net
Mon Apr 4 18:50:44 CEST 2016
> On Apr 4, 2016, at 9:22 AM, Janszen, Derek <derek.janszen at precisionformedicine.com> wrote:
>
> Hi,
>
> I want to create a data frame similar to the following, but greatly scaled up:
> df <- data.frame(aaa= c("a","b","c"), integer(3), integer(3))
> names(df)[2:3] <- paste("var",1:2,sep="")
> which yields
> aaa var1 var2
> 1 a 0 0
> 2 b 0 0
> 3 c 0 0
>
> setNames( data.frame( rep(list( 1:3), 5) ) , paste0("V", 1:5) )
V1 V2 V3 V4 V5
1 1 1 1 1 1
2 2 2 2 2 2
3 3 3 3 3 3
Or:
> data.frame( c( list( 'a'=letters[1:3] ), rep(list('x'=integer(3) ), 5) ))
a x x.1 x.2 x.3 x.4
1 a 0 0 0 0 0
2 b 0 0 0 0 0
3 c 0 0 0 0 0
Just replace the 3's and 5's with a number (possibly delivered via a named numeric vector of length-1) of your choosing.
--
David.
> I would not relish having to paste 'integer(3)' 5000 times :(
>
> So (I figure) there must be a way to do this programmatically, something akin to
> exp1 <- paste(rep("integer(3)",2),collapse=',')
> which looks like it might work: "integer(3),integer(3)" , as in the following
> df <- data.frame(aaa=xxx, eval(parse(text=exp1)))
> but this yields
>
> Error in parse(text = exp1) : <text>:1:11: unexpected ','
>
> 1: integer(3),
>
> ^
>
>
> Not sure just why this doesn't work (?parse does not help), but it's not important right now.
>
> I have used eval and parse in the past, but not in a way similar to what I'm trying to do now.
>
>
>
> exp1 <- rep("integer(3)",2) gives "integer(3)" "integer(3)"
>
> and upon parse(text=exp1) gives expression(integer(3), integer(3))
>
> which appears to be promising, and does not give an error in the following
>
> df <- data.frame(aaa=xxx, eval(parse(text=exp1)))
>
> but alas, does not give the desired result
> aaa eval.parse.text...exp1..
> 1 a 0
> 2 b 0
> 3 c 0
>
>
>
>
> I'm guessing that only the last evaluation of the expression is being evaluated, which I can understand.
>
> I feel certain that what I want to accomplish can be done programmatically, but am at a loss as to just how to do that.
> Chances are this has been covered before. If so, apologies.
> If not, can anyone point me to references with more info than the help pages, or suggest a solution? :)
>
> Thanks,
> Derek
>
> Derek Janszen, PhD
> Statistician, Analytics
>
> Precision for Medicine<http://www.precisionformedicine.com/>
> 8425 Progress Drive, Suite M | Frederick, MD 21701
> +1 240 415 6004 office
>
>
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David Winsemius
Alameda, CA, USA
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