NULL or a character vector giving the row
names for the data frame. Missing values are not allowed.
logical. If TRUE, setting row names and
converting column names (to syntactic names: see
make.names) is optional. Note that all of R's
base package as.data.frame() methods use
optional only for column names treatment, basically with the
meaning of data.frame(*, check.names = !optional).
in which variable should list item names be saved
additional arguments to be passed to or from methods.