[R] Help! What does this R command mean?

[Liaw, Andy]

":" 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]]
> >
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> 
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