"as.data.frame"(x, row.names = NULL, optional = FALSE, ...)NULL or a character vector giving the row
    names for the data frame.  Missing values are not allowed.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).