as.character（NA）的R值

Question

Does anybody know the internal value of as.character(NA)? How would somebody represent an NA string on the interpreter level? In other words, how would someone who would like to implement an R VM do that?

I looked in the sourcecode of R but I could not find an self-explaining definition of NA_STRING, which seems to be the underlying representation of string value of NA.

Thank in advance for all sugestions

Answer 1

根据Rinternals.h ， NA_STRING是CHARSXP ，它是“标量字符串类型（仅内部）”。