[R] Why can't R understand if(num!=NA)?

[arun]

 num1<- c(0,NA,1,3)
 num1==NA
#[1] NA NA NA NA
 num1!=NA
#[1] NA NA NA NA
 is.na(num1)
#[1] FALSE  TRUE FALSE FALSE
A.K.



----- Original Message -----
From: jpm miao <miaojpm at gmail.com>
To: r-help <r-help at r-project.org>
Cc: 
Sent: Friday, May 3, 2013 11:24 AM
Subject: [R] Why can't R understand if(num!=NA)?

I have a program, when I write

if(num!=NA)

it yields an error message.

However, if I write

if(is.na(num)==FALSE)

it works.

Why doesn't the first statement work?

Thanks,

Miao

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