[R] questions on some operators in R

[Greg Snow]

Just to expand a little on David's reply.

The & vs. && and | vs. || issue is really about where and how you plan to use things.  & and | work on vectors and are intended to be used to combine logical vectors into a new logical vector (that can be used for various things).  && and || are used for program control, mainly in the condition of if or while statements.  The program flow versions have the benefit of evaluating the left condition, then only evaluating the right condition if needed (this can save some warning messages and time).  Compare the following commands:

> x <- rnorm(100)
> any(x < 0) | any(log(x) < 0)
> any(x < 0) || any(log(x) < 0)


The '<-' operator is for assignment, the '=' is used to match formal arguments in functions to their values.  In some cases where it is unambiguous the '=' can be used in place of '<-' (see the help page).  But you need to understand the difference since there are cases where they will not do the same thing.

> mean( x <- rnorm(100) )
And
> mean( x = rnorm(100) )

Do not do the same thing (well part is the same, but there is a subtle but significant difference).

> mean( z <- rnorm(100) )
And
> mean( z = rnorm(100) )

Are even more different.



-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111


> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of li li
> Sent: Wednesday, June 16, 2010 4:33 PM
> To: r-help
> Subject: [R] questions on some operators in R
> 
> Hi all,
>    I have two questions. Can some one give some help?
> 
>    The first question is regarding the pair of operators "&" and "&&".
> What
> is the
> difference between the two?
> 
>    The second question is regarding "<-" and "=".  Usually we use
> "<-" as the assignment operator. I saw some people use "=". Is there
> any difference between the two.
> 
>      Thank you!!
>              Hannah
> 
> 	[[alternative HTML version deleted]]
> 
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