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 a mixed case?
> w <- list(a=5,b="xyz")
> wu <- unlist(w)
> class(wu)
[1] "character"
> wu
a b
"5" "xyz"Here, R chose the least common denominator: character strings. This sounds like some kind of precedence structure, and it is. As R’s help for unlist() states:
Where possible the list components are coerced to a common mode during the unlisting, and so the result often ends up as a character vector. Vectors will be coerced to the highest type of the components in the hierarchy NULL < raw < logical < integer < real < complex < character < list < expression: pairlists are treated as lists.
But there is something else to deal with here. Though wu is a vector and not a list, R did give each of the elements a name. We can remove them by setting their names to NULL, as you saw in Section 2.11.
> names(wu) <- NULL > wu [1] "5" "xyz"
We can also remove the elements’ names directly with unname(), as follows:
> wun <- unname(wu) > wun [1] "5" "xyz"
This also has the advantage of not destroying the names in wu, in case they are needed later. If they will not be needed later, we could simply assign back to wu instead of to wun in the preceding statement.