Hi all, Could anyone refer to me to a good source to learn how to program a simple control-flow construct* in R, or provide me with a simple example? Control-flow constructs are programmed as primitives, but I would like to be able to do that (if possible) in pure R. The general context is that those functions are a mystery to me. The motivating example is that I would like to create a function that behave similarly to base::`if` with an extra argument to the function (e.g. to include an error rate on the condition). Many thanks, Alex * control-flow constructs are functions such as if, for, while... that allow for call of the form fn(x) expr to work (see ?Control). -- Alexandre Courtiol http://sites.google.com/site/alexandrecourtiol/home *"Science is the belief in the ignorance of experts"*, R. Feynman [[alternative HTML version deleted]]
Hi Alexandre,
I'm not an R expert so this is only my personal thought:
I don't think you can achieve what you want exactly. A possible solution
would be defining a binary operator %*%, where you can replace the asterisk
with any function name you want. The function %*% is special since it has
two arguments, left operand and right operand respectively. You then
can call the `substitute` function to get its function arguments in an
expression format and proceed to do what you want. Here is an example to
show the idea.
*Code:*
`%myOperator%` <- function(x, y) {
x = substitute(x)
y = substitute(y)
return(list(x, y))
}
myIf(i == 1, arg1) %myOperator% {
doSomeThing
}
*Results:*
[[1]]
myIf(i == 1, arg1)
[[2]]
{
doSomeThing
}
I hope that helps.
Best,
Jiefei
On Sun, May 26, 2019 at 4:45 AM Alexandre Courtiol <
alexandre.courtiol at gmail.com> wrote:
> Hi all,
>
> Could anyone refer to me to a good source to learn how to program a simple
> control-flow construct* in R, or provide me with a simple example?
>
> Control-flow constructs are programmed as primitives, but I would like to
> be able to do that (if possible) in pure R.
>
> The general context is that those functions are a mystery to me. The
> motivating example is that I would like to create a function that behave
> similarly to base::`if` with an extra argument to the function (e.g. to
> include an error rate on the condition).
>
> Many thanks,
>
> Alex
>
> * control-flow constructs are functions such as if, for, while... that
> allow for call of the form fn(x) expr to work (see ?Control).
>
> --
> Alexandre Courtiol
>
> http://sites.google.com/site/alexandrecourtiol/home
>
> *"Science is the belief in the ignorance of experts"*, R. Feynman
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
[[alternative HTML version deleted]]
Thanks a lot Jiefei, I had thought of defining a binary operator (inspired by pipes) or simply using an additional condition in the if() calls [e.g. if(foo & fn(bar)) doSomeThing; with fn(bar) returning a logical], but both are workaround that I do not find as elegant as a proper control-flow construct. Thus two questions remain: - is it possible to create a control-flow construct in pure R? - if yes, how? Anyone with more insights? Thanks On Mon, 27 May 2019 at 04:27, King Jiefei <szwjf08 at gmail.com> wrote:> Hi Alexandre, > > I'm not an R expert so this is only my personal thought: > > I don't think you can achieve what you want exactly. A possible solution > would be defining a binary operator %*%, where you can replace the asterisk > with any function name you want. The function %*% is special since it has > two arguments, left operand and right operand respectively. You then > can call the `substitute` function to get its function arguments in an > expression format and proceed to do what you want. Here is an example to > show the idea. > > *Code:* > > `%myOperator%` <- function(x, y) { > x = substitute(x) > y = substitute(y) > return(list(x, y)) > } > > > myIf(i == 1, arg1) %myOperator% { > doSomeThing > } > > > *Results:* > > [[1]] > myIf(i == 1, arg1) > > [[2]] > { > doSomeThing > } > > I hope that helps. > > Best, > Jiefei > > On Sun, May 26, 2019 at 4:45 AM Alexandre Courtiol < > alexandre.courtiol at gmail.com> wrote: > >> Hi all, >> >> Could anyone refer to me to a good source to learn how to program a simple >> control-flow construct* in R, or provide me with a simple example? >> >> Control-flow constructs are programmed as primitives, but I would like to >> be able to do that (if possible) in pure R. >> >> The general context is that those functions are a mystery to me. The >> motivating example is that I would like to create a function that behave >> similarly to base::`if` with an extra argument to the function (e.g. to >> include an error rate on the condition). >> >> Many thanks, >> >> Alex >> >> * control-flow constructs are functions such as if, for, while... that >> allow for call of the form fn(x) expr to work (see ?Control). >> >> -- >> Alexandre Courtiol >> >> http://sites.google.com/site/alexandrecourtiol/home >> >> *"Science is the belief in the ignorance of experts"*, R. Feynman >> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> R-devel at r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-devel >> >-- Alexandre Courtiol http://sites.google.com/site/alexandrecourtiol/home *"Science is the belief in the ignorance of experts"*, R. Feynman [[alternative HTML version deleted]]