The Art of R Programming

Accessing List Components and Values

If the components in a list do have tags, as is the case with name, salary, and union for j in Section 4.1, you can obtain them via names():

> names(j)
[1] "name"   "salary" "union"

To obtain the values, use unlist():

> ulj <- unlist(j)
> ulj
   name  salary   union
  "Joe" "55000"  "TRUE"
> class(ulj)
[1] "character"

The return value of unlist() is a vector—in this case, a vector of character strings. Note that the element names in this vector come from the components in the original list.

On the other hand, if we were to start with numbers, we would get numbers.

> z <- list(a=5,b=12,c=13)
> y <- unlist(z)
> class(y)
[1] "numeric"
> y
 a  b  c
 5 12 13

So the output of unlist() in this case was a numeric vector. What about ...