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

[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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