# "if" function in pure R?

4 messages
Open this post in threaded view
|

## "if" function in pure R?

 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]] ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
Open this post in threaded view
|

## Re: "if" function in pure R?

 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 < [hidden email]> 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]] > > ______________________________________________ > [hidden email] mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel>         [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-devel