Creating a function in R with variable number of arguments,

Question

When creating a function in R, we usually specify the number of argument like

function(x,y){
}

That means it takes only two arguments. But when the numbers of arguments are not specified (For one case I have to use two arguments but another case I have to use three or more arguments) how can we handle this issue? I am pretty new to programming so example will be greatly appreciated.

instead of each variable, you could hand over one list containing all variables. The list can be any length. So x would be a list. — Linus
– Linus, Commented Feb 8, 2018 at 20:56

lefft · Accepted Answer · 2018-02-09 00:35:08Z

45

d <- function(...){
    x <- list(...) # THIS WILL BE A LIST STORING EVERYTHING:
    sum(...)       # Example of inbuilt function
}

d(1,2,3,4,5)

[1] 15

edited Feb 9, 2018 at 0:35

lefft

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answered Feb 8, 2018 at 21:02

Onyambu

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5 Comments

IceCreamToucan Over a year ago

Putting it in a list is probably appropriate for whatever Lzz0 wants to do, but fyi, in your example you could skip the list and unlist and just do sum(...)

Lzz0 Over a year ago

Thanks, but another thought came to my mind. What will the situation if I want to use a list for sum and another list for subtraction. I mean can I give two sets of list (the number of variables of each set are not specific).

Onyambu Over a year ago

You will need to update the question with examples. Or maybe ask a different question. I really cant understand what you mean. If you need to subtract two lists you can use Map

Lzz0 Over a year ago

Suppose, in your example if I put d (1,2,3,....10,11) whatever number, the last two number always give me their multiplication and others are their sums. I mean I want to return two output from one list of input.

Onyambu Over a year ago

d=function(...){x=list(...);c(sum=sum(unlist(head(x,-2))),prod=prod(unlist(tail(x,2))))} This will do the trick

C. Braun · Accepted Answer · 2018-02-08 21:03:16Z

22

You can use ... to specify an additional number of arguments. For example:

myfun <- function(x, ...) {
    for(i in list(...)) {
        print(x * i)
    }
}

> myfun(4, 3, 1)
[1] 12
[1] 4
> myfun(4, 9, 1, 0, 12)
[1] 36
[1] 4
[1] 0
[1] 48
> myfun(4)

answered Feb 8, 2018 at 21:03

C. Braun

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