In working through material on p.272 of MASS (4th ed.), I came across the following model formula: pet1.lm <- lm(Y ~ No/EP - 1, Petrol) I was at a loss to understand the use of "/" until I looked in "An Introduction [!] to R," where I found the explanation. My request is that more complete material on model formulae be lifted from "Introduction to R" (or elsewhere) and put into the main online help files. There are other useful notations that may not be well known. Since formulae are not limited to any particular function, perhaps an entry could be made under "Formula". More justification: The help for "lm" does not explain this notation, nor did I find a cross-reference to anything useful there. The R Reference Manual seems to explain functions only. The R Language Definition has no index entry for "formula" or "model formulae". Looking to print, neither the section on "model formula" on p.56 of MASS nor the section surrounding the above example explains the notation, nor could I find it in Dalgaard's book, nor in Maindonald and Braun. This seems too nice a feature to keep hidden in plain sight. -- Mike Prager, NOAA, Beaufort, NC * Opinions expressed are personal and not represented otherwise. * Any use of tradenames does not constitute a NOAA endorsement.
This isn't particularly helpful because the book is quite old but formula notation/functionality is covered in depth in "Statistical Models in S" by Chambers and Hastie. My guess is that there is strong consistency between what is said in there and how things work in R. On Fri, May 30, 2008 at 4:19 PM, Mike Prager wrote:> In working through material on p.272 of MASS (4th ed.), I came > across the following model formula: > > pet1.lm <- lm(Y ~ No/EP - 1, Petrol) > > I was at a loss to understand the use of "/" until I looked in > "An Introduction [!] to R," where I found the explanation. > My request is that more complete material on model formulae be > lifted from "Introduction to R" (or elsewhere) and put into the > main online help files. There are other useful notations that > may not be well known. Since formulae are not limited to any > particular function, perhaps an entry could be made under > "Formula". > > More justification: > > The help for "lm" does not explain this notation, nor did I find > a cross-reference to anything useful there. The R Reference > Manual seems to explain functions only. The R Language > Definition has no index entry for "formula" or "model formulae". > > Looking to print, neither the section on "model formula" on p.56 > of MASS nor the section surrounding the above example explains > the notation, nor could I find it in Dalgaard's book, nor in > Maindonald and Braun. > This seems too nice a feature to keep hidden in plain sight. > > -- > Mike Prager, NOAA, Beaufort, NC > * Opinions expressed are personal and not represented otherwise. > * Any use of tradenames does not constitute a NOAA endorsement. > > ______________________________________________ > R-devel at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel
Hi Mike,>> I was at a loss to understand the use of "/" until I looked in "An >> Introduction [!] to R," >> where I found the explanation.I am not with you on the [!], because the information is basically where you are "complaining" that it isn't, viz in your face --- i.e. in the introductory document ---, but the operator surely deserves a mention in ?formula. So on that score I agree with you. Best, Mark. Mike Prager wrote:> > In working through material on p.272 of MASS (4th ed.), I came > across the following model formula: > > pet1.lm <- lm(Y ~ No/EP - 1, Petrol) > > I was at a loss to understand the use of "/" until I looked in > "An Introduction [!] to R," where I found the explanation. > > My request is that more complete material on model formulae be > lifted from "Introduction to R" (or elsewhere) and put into the > main online help files. There are other useful notations that > may not be well known. Since formulae are not limited to any > particular function, perhaps an entry could be made under > "Formula". > > More justification: > > The help for "lm" does not explain this notation, nor did I find > a cross-reference to anything useful there. The R Reference > Manual seems to explain functions only. The R Language > Definition has no index entry for "formula" or "model formulae". > > Looking to print, neither the section on "model formula" on p.56 > of MASS nor the section surrounding the above example explains > the notation, nor could I find it in Dalgaard's book, nor in > Maindonald and Braun. > > This seems too nice a feature to keep hidden in plain sight. > > -- > Mike Prager, NOAA, Beaufort, NC > * Opinions expressed are personal and not represented otherwise. > * Any use of tradenames does not constitute a NOAA endorsement. > > ______________________________________________ > R-devel at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > >-- View this message in context: http://www.nabble.com/Request%3A-Documentation-of-formulae-tp17567491p17568035.html Sent from the R devel mailing list archive at Nabble.com.
Mike Prager <mike.prager at noaa.gov> wrote:> I was at a loss to understand the use of "/" until I looked in > "An Introduction [!] to R," where I found the explanation. > > My request is that more complete material on model formulae be > lifted from "Introduction to R" (or elsewhere) and put into the > main online help files.I also request the R Core consider remaining "An Introduction to R" to something like "R User's Guide." It spans 100 pages and treats many topics far beyond the introductory level. I was surprised at the wealth of information it contains, and I expect that I would have checked it first, not last, among available resources had it been more accurately named. -- Mike Prager, NOAA, Beaufort, NC * Opinions expressed are personal and not represented otherwise. * Any use of tradenames does not constitute a NOAA endorsement.
Rather than transport quantities of the Introduction to R (a perfectly sensible title for a very good starting point, IMHO) would it not be simpler and involve less maintenance to include a link or cross-reference in the 'formula' help page to the relevant part of the Introduction? If nothing else, that might get folk to look at the Introduction if they've bypassed it .... Steve E>>> Martin Maechler <maechler at stat.math.ethz.ch> 03/06/2008 07:48:46 >>> >>>>> "MP" == Mike Prager <mike.prager at noaa.gov>MP> Mike Prager <mike.prager at noaa.gov> wrote: >> I was at a loss to understand the use of "/" until I looked in >> "An Introduction [!] to R," where I found the explanation. >> >> My request is that more complete material on model formulae be >> lifted from "Introduction to R" (or elsewhere) and put into the >> main online help files. ******************************************************************* This email and any attachments are confidential. Any use...{{dropped:8}}