[R] Help! What does this R command mean?
andy_liaw at merck.com
Tue Jan 31 22:44:49 CET 2006
":" in a formula is not the same as ":" otherwise!
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
> 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,
> > Thanks a lot!
> > [[alternative HTML version deleted]]
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