[Rd] turning expression object to function
Dear all, I have the following problem. Given an expression object 'expr' containing a certain set of symbols (say 'a', 'b', 'c'), I would like to translate the expression object in an R function of, say, 'a', programmatically. Here an example of what I mean. Given: expr - expression(a+b+c) a call like: asFunctionOf(expr, 'a', list(b=1, c=2)) should return a function (not necessarly formally) equivalent to function(a) a+1+2 Some suggestions? Best regards, Antonio. __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] turning expression object to function
On Mon, 2006-12-18 at 19:06 +0100, Antonio, Fabio Di Narzo wrote: Dear all, I have the following problem. Given an expression object 'expr' containing a certain set of symbols (say 'a', 'b', 'c'), I would like to translate the expression object in an R function of, say, 'a', programmatically. Here an example of what I mean. Given: expr - expression(a+b+c) a call like: asFunctionOf(expr, 'a', list(b=1, c=2)) should return a function (not necessarly formally) equivalent to function(a) a+1+2 Some suggestions? Best regards, Antonio. Let me offer some pointers and a couple of possible examples: ?call ?as.function ?alist ?eval ?parse expr - expression(a + b + c) as.function(alist(a = , b = 1, c = 2, eval(expr)))(5) [1] 8 as.function(alist(a = , b = 1, c = 2, eval(expr)))(5, 10, 8) [1] 23 MyExpr - paste(letters[1:3], collapse = + ) MyExpr [1] a + b + c as.function(alist(a = , b = 1, c = 2, eval(parse(text = MyExpr(6) [1] 9 HTH, Marc Schwartz __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Re: [Rd] turning expression object to function
Here is one possibility. It does not use the second argument in your function
call but instead assumes the arguments of the output function are
those variables
in the expression that have not been assigned in the list L in the
order encountered.
library(gsubfn)
asFun - function(e, L = NULL, env = parent.frame()) {
fo - ~ x
fo[[2]] - e[[1]]
fun - fn$force(as.formula(do.call(substitute, list(fo, L
environment(fun) - env
fun
}
asFun(expression(a+b+c), list(b = 1, c = 2)) # function (a) a + 1 + 2
On 12/18/06, Antonio, Fabio Di Narzo [EMAIL PROTECTED] wrote:
Dear all,
I have the following problem.
Given an expression object 'expr' containing a certain set of symbols
(say 'a', 'b', 'c'), I would like to translate the expression object
in an R function of, say, 'a', programmatically. Here an example of
what I mean.
Given:
expr - expression(a+b+c)
a call like:
asFunctionOf(expr, 'a', list(b=1, c=2))
should return a function (not necessarly formally) equivalent to
function(a) a+1+2
Some suggestions?
Best regards,
Antonio.
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Re: [Rd] turning expression object to function
This is what I tried, and it seemed to work, but maybe others can give better ideas, and also explain why the first attempt to assign the formal arguments didn't work (but the second did.) f - function() NULL formals(f) - list(b=1, c=2) f function (b = 1) 2 formals(f) - list(b=1, c=2) f function (b = 1, c = 2) 2 body(f) [1] 2 body(f) - expression(a+b+c) f function (b = 1, c = 2) a + b + c a - 3 f() [1] 6 One thing you may want to be careful of is the environment of the function. (If I don't start out with f having a NULL body, the first attempt to assign the formals works.) -- Tony Plate sessionInfo() R version 2.4.0 (2006-10-03) i386-pc-mingw32 locale: LC_COLLATE=English_United States.1252;LC_CTYPE=English_United States.1252;LC_MONETARY=English_United States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252 attached base packages: [1] methods stats graphics grDevices utils datasets [7] base other attached packages: MASS foreign 7.2-29 0.8-17 Antonio, Fabio Di Narzo wrote: Dear all, I have the following problem. Given an expression object 'expr' containing a certain set of symbols (say 'a', 'b', 'c'), I would like to translate the expression object in an R function of, say, 'a', programmatically. Here an example of what I mean. Given: expr - expression(a+b+c) a call like: asFunctionOf(expr, 'a', list(b=1, c=2)) should return a function (not necessarly formally) equivalent to function(a) a+1+2 Some suggestions? Best regards, Antonio. __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel __ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
