Is the %>%
pipe operator always feeding the left-hand side (LHS) to the first argument of the right-hand side (RHS)? Even if the first argument is specified again in the RHS call?
Say I want to specify which variable to use in cor()
:
library(magrittr)
iris %>%
cor(x=.$Sepal.Length, y=.$Sepal.Width)
But this fails, it looks like it call something like cor(., x=.$Sepal.Length, y=.$Sepal.Width)
?
I know I could use instead
iris %$%
cor(x=Sepal.Length, y=Sepal.Width)
But wanted to find a solution with %>%
...
Is the
%>%
pipe operator always feeding the left-hand side (LHS) to the first argument of the right-hand side (RHS)? Even if the first argument is specified again in the RHS call?
No. You’ve noticed the exception yourself: if the right-hand side uses .
, the first argument of the left-hand side is not fed in. You need to pass it manually.
However, this is not happening in your case because you’re not using .
by itself, you’re using it inside an expression. To avoid the left-hand side being fed as the first argument, you additionally need to use braces:
iris %>% {cor(x = .$Sepal.Length, y = .$Sepal.Width)}
Or:
iris %$% cor(x = Sepal.Length, y = Sepal.Width)
— after all, that’s what %$%
is there for, as opposed to %>%
.
But compare:
iris %>% lm(Sepal.Width ~ Sepal.Length, data = .)
Here, we’re passing the left-hand side expression explicitly as the data
argument to lm
. By doing so, we prevent it being passed as the first argument to lm
.