Edit: Apparently, I was mistaken. Turns out using .x is the recommended approach. See the post by @andresrcs below.
@Andrzej You can but it's better practice to use . for the single argument case.
From the purrr documentation:
.f
A function, formula, or vector (not necessarily atomic).
If a function, it is used as is.
If a formula, e.g. ~ .x + 2, it is converted to a function. There are three ways to refer to the arguments:
For a single argument function, use .
For a two argument function, use .x and .y
For more arguments, use ..1, ..2, ..3 etc