[R] Missing values

[Stephen Liu]

Hi folks,


Could you please help me to understand;


An Introduction to R
http://cran.r-project.org/doc/manuals/R-intro.html#Logical-vectors


The function is.na(x) gives a logical vector of the same size as x with value 
TRUE if and only if the corresponding element in x is NA.

     > z <- c(1:3,NA);  ind <- is.na(z)

and


Note that there is a second kind of “missing” values which are produced by 
numerical computation, the so-called Not a Number, NaN, values. Examples are

     > 0/0

or

     > Inf - Inf


the explanation being abstract to me to understand.  TIA


B.R.
Stephen L