Proper way to access list elements in R

Question

I am trying to make a list and access it's cells later in R. I am new to R and have a Matlab background. These [], [[]] are really bugging me. I tried reading the help and online but I still don't get it. In the following code c["var1"][1] returns differently than c$"var"[1].

What are the actual uses for these three notations [], [[]], $?

v <- vector("character", 5)
v[1] <- 'a'
v[2] <- 'a'
v[4] <- 'a'
v
# [1] "a" "a" ""  "a" "" 
c <- list(v, v)
names(c) <- c("var1", "var2")
c
# $var1
# [1] "a" "a" ""  "a" "" 

# $var2
# [1] "a" "a" ""  "a" "" 

c["var1"][1]
# $var1
# [1] "a" "a" ""  "a" "" 

c$"var1"[1]
# [1] "a"

Use `str` to see the structure of an object. See for instance `str(c[1])` opposed to `str(c[[1]])`. No need of quotes when using `$`: `c$var1` works just fine. — nicola, Sep 28 '15 at 09:26
Can you confirm that you have read `help("[")` and section 6.1 of [An Introduction to R](https://cran.r-project.org/doc/manuals/R-intro.pdf)? — Roland, Sep 28 '15 at 09:27

score 42 · Accepted Answer · answered Sep 28 '15 at 09:27

All these methods give different outputs

[ ] returns a list

[[ ]] returns the object which is stored in list

If it is a named list, then

List$name or List[["name"]] will return same as List[[ ]]

While List["name"] returns a list, Consider the following example

> List <- list(A = 1,B = 2,C = 3,D = 4)
> List[1]
$A
[1] 1

> class(List[1])
[1] "list"
> List[[1]]
[1] 1
> class(List[[1]])
[1] "numeric"
> List$A
[1] 1
> class(List$A)
[1] "numeric"
> List["A"]
$A
[1] 1

> class(List["A"])
[1] "list"
> List[["A"]]
[1] 1
> class(List[["A"]])
[1] "numeric"

Proper way to access list elements in R

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