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2.9651
2005 Feb 23
1
model.matrix for a factor effect with no intercept
I was surprised by this (in R 2.0.1):
> a <- ordered(-1:1)
> a
[1] -1 0 1
Levels: -1 < 0 < 1
> model.matrix(~ a)
(Intercept) a.L a.Q
1 1 -7.071068e-01 0.4082483
2 1 -9.073800e-17 -0.8164966
3 1 7.071068e-01 0.4082483
attr(,"assign")
[1] 0 1 1
attr(,"contrasts")
attr(,"contrasts")$a
[1]