#缺失值 Missing Value
> #NaN不可识别NA > x <- c(1,NA,2,NA,3)
> is.na(x) [1] FALSE TRUE FALSE TRUE FALSE
> is.nan(x) [1] FALSE FALSE FALSE FALSE FALSE
> #NA可识别NaN > y <- c(1,NaN,2,NaN,3)
> is.na(y) [1] FALSE TRUE FALSE TRUE FALSE
> is.nan(y) [1] FALSE TRUE FALSE TRUE FALSE