[R] Help! What does this R command mean?
Ionut Florescu
ifloresc at stevens.edu
Tue Jan 31 22:09:54 CET 2006
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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