At 07:13 PM 2/4/2004 -0600, Douglas Bates wrote:
John Fox <[EMAIL PROTECTED]> writes:
> At 06:07 PM 2/4/2004 +0100, Martin Maechler wrote: > > >>>>> "JohnF" == John Fox <[EMAIL PROTECTED]> > > >>>>> on Wed, 04 Feb 2004 09:20:43 -0500 writes: > > > > JohnF> Dear Philippe, I suppose that you want a histogram > > JohnF> for snow.cover and not for year. There are several > > JohnF> ways to proceed; two are > > > > JohnF> hist(mydata$snow.cover) > > > > JohnF> and > > > > JF> attach(mydata) > > JF> hist(snow.cover) > > > >Actually, attaching data frames is a bit discouraged these days. > >The modern R way for this (and more complicated situations) is > > > > with(mydata, hist(snow.cover) ) > > > > Although I'm aware of (some of) the problems and possibly confusing > situations that can arise from attaching a data frame, I believe that, > especially for novice users, there's an advantage in doing so. In > particular, although using with() is perhaps less ambiguous, it is > necessary to repeat it for each command.
But with any version of R compiled with the readline library and with the Windows GUI and with ESS for emacs you can use the arrow keys to retrieve the last line typed then edit it. Repeating information from earlier lines is not terribly difficult.
I use the with(datafr, func(colname)) paradigm in live sessions for introductory classes and I don't find it overly cumbersome.
The with() mechanism has much to recommend it. In particular, it makes you think about where the data for a computation are coming from. I don't believe that this is necessarily an advantage,. however, for a novice user, who I believe will find it easier to attach a data frame, compute new variables in the global environment, and not have to think about where the data are coming from. Sometimes that can cause problems, but I believe that it's usually a simpler way to proceed. On the other hand, I can see the argument for encouraging good habits from the start.
Regards, John ----------------------------------------------------- John Fox Department of Sociology McMaster University Hamilton, Ontario, Canada L8S 4M4 email: [EMAIL PROTECTED] phone: 905-525-9140x23604 web: www.socsci.mcmaster.ca/jfox
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