In some cases, str() does not print the "names" attribute of the object: u <- structure(c(5, 6), names = c("a", "b"), color = "blue") str(u) # atomic [1:2] 5 6 # - attr(*, "color")= chr "blue" Is it a bug or a design choice? Originally asked here: https://stackoverflow.com/q/47185756/6656269