From ggrothendieck at gmail.com  Tue Jan 31 22:55:25 2006
From: ggrothendieck at gmail.com (Gabor Grothendieck)
Date: Tue, 31 Jan 2006 16:55:25 -0500
Subject: [Rd] [R] Help! What does this R command mean?
In-Reply-To: <39B6DDB9048D0F4DAD42CB26AAFF0AFAFED79A@usctmx1106.merck.com>
References: <39B6DDB9048D0F4DAD42CB26AAFF0AFAFED79A@usctmx1106.merck.com>
Message-ID: <971536df0601311355g7a4e9337iab7e356e533bcfee@mail.gmail.com>

I think that a pointer to ?formula needs to be added to ?":"


On 1/31/06, Liaw, Andy <andy_liaw at merck.com> wrote:
> ":" in a formula is not the same as ":" otherwise!
>
> Andy
>
> From: Ionut Florescu
> >
> > a:b means - all the element in the vector from a to b
> > a[,-1] means for the matrix a keep all the rows but not the last or
> > first -can't remember column.
> > When in doubt do what I do make a small matrix and apply the
> > command see
> > what it does.
> > After this:
> >  > a=matrix(c(1:9),3,3)
> >  > a[,-1]
> >      [,1] [,2]
> > [1,]    4    7
> > [2,]    5    8
> > [3,]    6    9
> >
> > you see that -1 eliminates the first column.
> > I found the R manual useless myself.
> > The only thing useful is the search function in the html
> > help. That has
> > examples.
> >
> > Ionut Florescu
> >
> > Michael wrote:
> > > Hi all,
> > >
> > > R is so difficult. I am so desperate.
> > >
> > > What does the ":" mean in the following statement?
> > >
> > > What does the "[, -1]" mean?
> > >
> > >
> > >> # Leaps takes a design matrix as argument: throw away the intercept
> > >> # column or leaps will complain
> > >>
> > >> X <- model.matrix(lm(V ~ I + D + W +G:I + P + N,
> > election.table))[,-1]
> > >>
> > >
> > > Thanks a lot!
> > >
> > >     [[alternative HTML version deleted]]
> > >
> > > ______________________________________________
> > > R-help at stat.math.ethz.ch mailing list
> > > https://stat.ethz.ch/mailman/listinfo/r-help
> > > PLEASE do read the posting guide!
> > http://www.R-project.org/posting-guide.html
> > >
> > >
> >
> > ______________________________________________
> > R-help at stat.math.ethz.ch mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide!
> > http://www.R-project.org/posting-guide.html
> >
> >
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
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> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
>



[Rd] [R] Help! What does this R command mean?
Gabor Grothendieck