Why does sapply() return a list with attributes when used on characters?

Question

There is a strange behaviour of sapply() when used on a vector of characters:

y <- c("Hello", "bob", "daN")
z <- sapply(y, function(x) {toupper(x)})
z
# Hello     bob     daN 
# "HELLO"   "BOB"   "DAN" 
str(z)
# Named chr [1:3] "HELLO" "BOB" "DAN"
# - attr(*, "names")= chr [1:3] "Hello" "bob" "daN"

Why does sapply() return a vector with the old values as attributes? I don't want them, I don't need them and I am not aware of this behaviour when applied on e.g. numerical vectors.

Answer 1

By default, sapply() adds names for each iteration on character vectors. The result can be delivered without the names by using USE.NAMES = FALSE in the call.

sapply(y, toupper, USE.NAMES = FALSE)
# [1] "HELLO" "BOB"   "DAN" 

This is explained in help(sapply)

USE.NAMES - logical; if TRUE and if X is character, use X as names for the result unless it had names already. Since this argument follows ... its name cannot be abbreviated.

Note that when you are applying a single function only, there is no need to use an anonymous function (anonymous function usage is also slightly less efficient). This is also shown above.

Also note that sapply() is not necessary here, as toupper() is vectorized.

toupper(y)
# [1] "HELLO" "BOB"   "DAN"