CODEWITHSUNDEEP
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jslefche
jslefche

Reputation: 4599

Define new operator for tilde / formula

I'm trying to code a new operator, a double tilde ~~, to denote a different kind of formula to be passed onto another function (e.g., mirroring the functionality of ~~ in the lavaan package lavaan syntax).

The issue is y ~~ x returns y ~ ~x, where the second ~ is returned with the predictors.

I am at a total loss here. It seems ~ is a primitive function .Primitive("~") with no methods, unlike, say, +. So existing tutorials for S3 methods are useless.

Is this a dead end and am I doing something really against the programming language? Or is there an easy solution I am missing?

Upvotes: 2

Views: 158

Answers (1)

Drey
Drey

Reputation: 3364

I guess, if you accept the comment, I can make an answer out of it:

~ is an operator in R like +,-, /,*. Although it is possible to use many kinds of characters for your variables using ticks `xxx` and qoute "xxx" you also need to access them with ticks (see ?Reserved). (I'm gonna use quotes instead of ticks here, but consider using ticks for a more accepted style guide.)

R is a functional programming language and therefore you can access every single language statement as a function, e.g. a + b is the same as "+"(a, b). When you write a + b it is just syntactic sugar - language-wise it is translated into a primitive function call with two arguments.

To complicate things, there is an order of evaluation. So if you write a~~b it gets translated into "~"(a, ~b). It is because ~ is a primitive operator desiged as a sigle character. You still can define the function "~~" <- function(a,b) {a + b}, but you can only call it by "~~"(a,b) directly for it to work.

On the other hand, you need to be able to specify how a binary operator looks like. Having defined a function "asdf" <- function(a,b) {a + b} is not enough and this will not work: a asdf b

R has something to define binary operators (R: What are operators like %in% called and how can I learn about them?), see large portion of binary operators used like in magrittr's %>% or doParallel's %dopar%. Thus it is better to stick to the binary operator syntax using %, i.e. <tick>%~~%<tick> <- function(a,b) {a+b}. Then you can easily access it by using syntactic sugar a %~~% b.

Strange stuff, I agree. As for magic tricks: try this at home "for"(a, 1:10, {print(a)}). Bonus question: why is a visible in the parent frame ?

Upvotes: 1

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