Hello, Does anyone know of a function that will determine whether or not a formula object has a left hand side? I.e., can differentiate between y ~ x + z and ~ x + z Perhaps I'm overlooking the obvious... Thanks!
attr(terms(formula), "response") is 1 if the formula has a left hand side and 0 otherwise. At a lower level, you can look at length(formula): 2 means there is no LHS, 3 means there is (any other value indicates that someone made a call object that the parser would not make). Bill Dunlap Spotfire, TIBCO Software wdunlap tibco.com> -----Original Message----- > From: r-help-bounces at r-project.org > [mailto:r-help-bounces at r-project.org] On Behalf Of Erik Iverson > Sent: Monday, December 13, 2010 12:17 PM > To: R-help > Subject: [R] Does a formula object have a "left hand side" > > Hello, > > Does anyone know of a function that will determine whether > or not a formula object has a left hand side? > > I.e., can differentiate between > > y ~ x + z > > and > > ~ x + z > > Perhaps I'm overlooking the obvious... > > Thanks! > > ______________________________________________ > R-help at 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. >
Erik -
Perhaps the "response" attribute of the terms() function?
> formula1 = formula(y ~ x + z)
> formula2 = formula(~x + z)
> attr(terms(formula1),'response')
[1] 1> attr(terms(formula2),'response')
[1] 0
Although there may be more direct ways.
- Phil Spector
Statistical Computing Facility
Department of Statistics
UC Berkeley
spector at stat.berkeley.edu
On Mon, 13 Dec 2010, Erik Iverson wrote:
> Hello,
>
> Does anyone know of a function that will determine whether
> or not a formula object has a left hand side?
>
> I.e., can differentiate between
>
> y ~ x + z
>
> and
>
> ~ x + z
>
> Perhaps I'm overlooking the obvious...
>
> Thanks!
>
> ______________________________________________
> R-help at 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.
>