R中的地图调用深度似乎不太直观

Question

It seems that the natural depth of the map function in R is not what one would expect.

Reprex:

data = list(
  a =list(
    '1' <- c(1, 2),
    '2' <- c(3,4)
    ),
  b = list(
    '3' <- c(5,6),
    '4' <- c(7,8)
  ) 
)

I want to uppercase the names of the list and print them out, but this doesn't work.

map(data, ~str_to_upper(names(.x)))

Instead I have to do this:

map_depth(data,.depth = 0, ~str_to_upper(names(.x)))

Thanks in advance for the help.

Answer 1

The input to map is the underlying list which for first iteration is

data[[1]]
#[[1]]
#[1] 1 2

#[[2]]
#[1] 3 4

This has no names in it hence it fails.

When you pass

map_depth(data,.depth = 0, ~str_to_upper(names(.x)))

The input for first iteration is

data[1]
#$a
#$a[[1]]
#[1] 1 2

#$a[[2]]
#[1] 3 4

which has names and hence it prints them.

You can directly use

stringr::str_to_upper(names(data))
#[1] "A" "B"

Or in base R

toupper(names(data))