On Jul 3, 2012, at 4:10 PM, mms...@comcast.net wrote:
Hello,
I want to create a design matrix using R. Can you explain the code
which creates the following please? I understand the first part.
What first part if the next part is ... this ?
b=g1(?) does what?
That's just generating a factor variable.
dd <- data.frame(a = gl(3,4), b = gl(4,1,12)) # balanced 2-way
dd
a b
1 1 1
2 1 2
3 1 3
4 1 4
5 2 1
6 2 2
7 2 3
8 2 4
9 3 1
10 3 2
11 3 3
12 3 4
I am using the tree dataset in R. I want to form a reparameterized
design matrix in ones, zeroes and minus ones. The dataframe dd is
very important here.
Can anyone assist here? Thanks in advance.
Something like this?
model.matrix(~a+b, data= dd, contrasts = list(a="contr.sum",
b="contr.sum") )
(Intercept) a1 a2 b1 b2 b3
1 1 1 0 1 0 0
2 1 1 0 0 1 0
3 1 1 0 0 0 1
4 1 1 0 -1 -1 -1
5 1 0 1 1 0 0
6 1 0 1 0 1 0
7 1 0 1 0 0 1
8 1 0 1 -1 -1 -1
9 1 -1 -1 1 0 0
10 1 -1 -1 0 1 0
11 1 -1 -1 0 0 1
12 1 -1 -1 -1 -1 -1
attr(,"assign")
[1] 0 1 1 2 2 2
attr(,"contrasts")
attr(,"contrasts")$a
[1] "contr.sum"
attr(,"contrasts")$b
[1] "contr.sum"
--
David Winsemius, MD
West Hartford, CT
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