Avoid using "eval" in a neat way

This has been discussed extensively, on this list as well as
elsewhere. I suggest doing a web search, read up on the issue, and
post back here only if you have specific questions that are not
answered already.

Best,
Ista

I know using eval is not optimal and maybe bad, but how to avoid using eval
in the following example

func1 <- function(dat, eval.this) {
    eval(parse(text = paste0("with(dat, ", eval.this, ")")))
}

dat <- data.frame(x = 1:2, y = 2:3)

func1(dat, "x*2+y")

func1(dat, "sin(x)*cos(y)")

Here eval.this is a string that contains whatever the user wants to
evaluate. I wonder whether there is a neat way to avoid using eval in this
case? So far I have not figured out a way to do this.

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I know using eval is not optimal and maybe bad, but how to avoid using eval
in the following example

func1 <- function(dat, eval.this) {
     eval(parse(text = paste0("with(dat, ", eval.this, ")")))
}

dat <- data.frame(x = 1:2, y = 2:3)

func1(dat, "x*2+y")

func1(dat, "sin(x)*cos(y)")

Here eval.this is a string that contains whatever the user wants to
evaluate. I wonder whether there is a neat way to avoid using eval in this
case? So far I have not figured out a way to do this.

You're asking how to parse some text and evaluate it without using eval. 
Sounds impossible to me.

Duncan Murdoch

You have set up your criteria for success to be that your user has full freedom to specify code in strings to evaluate. Then you ask how to achieve this goal without evaluating that code. Are you thinking objectively at all about your question?

The advice to not use eval has a number of justifications that you should be able to find yourself online (unnecessary obfuscation and program security are two). Implementing an interpreter is not where this advice applies.

At the core of this problem, as long as you accept that your user is working within the R interpreter then they can provide your code with functions that access data on their own. You don't need to assume so much responsibility as your question assumes you have to.

"Doctor, my head hurts!"
"Then stop banging it against the wall."
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I know using eval is not optimal and maybe bad, but how to avoid using
eval
in the following example

func1 <- function(dat, eval.this) {
   eval(parse(text = paste0("with(dat, ", eval.this, ")")))
}

dat <- data.frame(x = 1:2, y = 2:3)

func1(dat, "x*2+y")

func1(dat, "sin(x)*cos(y)")

Here eval.this is a string that contains whatever the user wants to
evaluate. I wonder whether there is a neat way to avoid using eval in
this
case? So far I have not figured out a way to do this.

[[alternative HTML version deleted]]

______________________________________________
R-help at 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.

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