Help! What does this R command mean?

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!

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