Thank you all for your kind reply! Hannah 2010/6/18 Greg Snow <greg.s...@imail.org>
> 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.s...@imail.org > 801.408.8111 > > > > -----Original Message----- > > From: r-help-boun...@r-project.org [mailto:r-help-boun...@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]] > > > > ______________________________________________ > > R-help@r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide > > http://www.R-project.org/posting-<http://www.r-project.org/posting-> > > guide.html > > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.