[R] Missing values

[Stephen Liu]

----- Original Message ----

From: Michael Bedward <michael.bedward at gmail.com>
To: Stephen Liu <satimis at yahoo.com>
Cc: r-help at r-project.org
Sent: Tue, August 17, 2010 3:57:05 PM
Subject: Re: [R] Missing values

>NA is a value that you can use for "missing" or inapplicable. It is
>also the value returned by R functions to indicate missing (e.g. if
>you use the match function to search a vector for a particular value,
>but the value isn't present, match will return NA).

H Michael,

I understand above explanation.

I don't understand follow;

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)


>?is.na
....
Usage:

     NA
     is.na(x)
     ## S3 method for class 'data.frame':
     is.na(x)
     
     is.na(x) <- value
....


>NaN means that the value wasn't missing but can't be expressed as a
>number. 0/0 is NaN because the result is mathematically undefined
>(sometimes called 'indeterminate').

What is following expression;

> Inf - Inf

?

TIA


B.R.
Stephen L