In R, in list(), the first name is surrounded by `` automatically, Why?

Question

In the list, the first component has automatically endowed ``, why ? I think it should be $f instead of $`f`.

> list(f=c(1,2),h=c(1,2))
$`f`
[1] 1 2

$h
[1] 1 2

Answer 1

This will happen if you use numeric values as list elements names. This is done to clearly differentiate the list indices (e.g. list[1]) from the list names (e.g. list$'1' - wrong quotes du to formatting here).

In your example:

list <- list(f=c(1,2),h=c(1,2))
$f
[1] 1 2

$h
[1] 1 2

The elements f and h can be accessed through naming or indexing:

# Naming
list$f
[1] 1 2

# Indexing
list[1]
$f
[1] 1 2

# Indexing (alternative)
list[[1]]
[1] 1 2

On the other hand, if your list names have numbers they will be coerced as non-numeric values to avoid confusion:

list <- list("2"=c(1,2),h=c(1,2))
$`2`
[1] 1 2

$h
[1] 1 2

# Naming
list$`2`
[1] 1 2

# Indexing
list[1]
$`2`
[1] 1 2

# Indexing (alternative)
list[[1]]
[1] 1 2