CODEWITHSUNDEEP
rnamespacesdplyrpipingmagrittr
agenis
agenis

Reputation: 8377

operator precedence for function called by namespace in piping

Please someone could explain why there is a difference in the behaviour of the last line of code, when I call a function using its namespace in a pipe, and what the error message actually means:

library(magrittr)
1:5 %>% cumsum
#### [1]  1  3  6 10 15
1:5 %>% cumsum()
#### [1]  1  3  6 10 15
1:5 %>% base::cumsum()
#### [1]  1  3  6 10 15
1:5 %>% (base::cumsum)
#### [1]  1  3  6 10 15
1:5 %>% base::cumsum
#### Error in .::base : unused argument (cumsum)

I genuinely thought that it would work since operator precedence rules state that the highest priority is for the namespace operator ::, far away from special operators.

Thanks.

Upvotes: 2

Views: 130

Answers (1)

Jan Sila
Jan Sila

Reputation: 1593

I think it is because it calls the description of the function, base::cumsum returns function (x) .Primitive("cumsum") which does not take any argument, which is what the error says. Once you add the () as you see a line above, it calls the function with the 1:5 argument.

Even better example is with your own function. 

foo<-function(){cat("hello")}

then returns its code if called without argument:

    > foo
function(){cat("hello")}

So it is similar with base::cumsum, but I guess it is somehow protected or just programmed that is gives you that description.

Upvotes: 3

Related Questions