[R] what is the meaning of this error message?

[Jim Lemon]

Inchallah Yarab wrote:
> Hi,
> I need your help :: what i the meaning of this error message"Missing value where true / false needed??"
>
>   
Hi Inchallah,
This usually happens when you have a conditional (if or while) statement 
like this:

if(var81 == 0) { ... }
while(var73 > 0) { ... }
ifelse(var13, ...)

If one of the variables resolves to NA, you will get that error message.

Jim