Subtraction method as variable

Question

Is it possible to assign subtraction (or division) in R as object and to call it? So that following example produce -1

a <- 1
b <- 2

method <- "-"
a method b
# Wanted result -1

method <- "/"
a method b
# Wanted result 0.5

Why I need this
I want to set function parameter to either - or /. Something like that:

dummyF <- function(a, b, method) {
    a get(method) b
}

Would `dummyF <- function(a, b, method) { txt = paste(a, method, b); eval(parse(text=txt)) }` suit your needs? — tblznbits, Apr 18 '16 at 16:50
If you only have two possible methods, you might want to hard-code them and then make selection a TRUE/FALSE option, like `function(a, b, do_plus) (if (do_plus) \`+\` else \`/\`)(a, b)` — Frank, Apr 18 '16 at 17:11

score 8 · Accepted Answer · answered Apr 18 '16 at 16:48

8

You can use backticks and then call the function using normal function notation, not infix notation:

foo <- `-`
foo(1,2)

An example with them in a list:

l <- list(add = `+`,subtract = `-`)
> l[["add"]](1,2)
[1] 3
> l[["subtract"]](1,2)
[1] -1

answered Apr 18 '16 at 16:48

joran

akrun · Answer 2 · 2016-04-18T16:55:50.500

6

We can use do.call

method <- "-"
do.call(method, list(a,b))
#[1] -1

method <- "/"
do.call(method, list(a,b))
#[1] 0.5

edited Apr 18 '16 at 16:55

answered Apr 18 '16 at 16:49

akrun

2 Answers2