design matrix construction question
On Nov 2, 2009, at 10:40 PM, Ben Bolker wrote:
with the following simple data frame
dd = structure(list(z = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L
), .Label = c("a", "b"), class = "factor"), x = c(0.3, 0.2, 0.1,
0, 0, 0, 0.2, 0.3)), .Names = c("z", "x"), row.names = c(NA,
-8L), class = "data.frame")
I would like know if it's possible to use model.matrix()
to construct the following design matrix in some sensible way:
za zb
1 1 0
2 1 0
3 1 0
4 0 0
5 0 0
6 0 0
7 0 1
8 0 1
How about something like this? dd$xf <- (dd$x > 0) + 0 model.matrix(~ z:xf - 1, dd) za:xf zb:xf 1 1 0 2 1 0 3 1 0 4 0 0 5 0 0 6 0 0 7 0 1 8 0 1 attr(,"assign") [1] 1 1 attr(,"contrasts") attr(,"contrasts")$z [1] "contr.treatment"
thanks Ben Bolker
Ken Knoblauch Inserm U846 Stem-cell and Brain Research Institute Department of Integrative Neurosciences 18 avenue du Doyen L?pine 69500 Bron France tel: +33 (0)4 72 91 34 77 fax: +33 (0)4 72 91 34 61 portable: +33 (0)6 84 10 64 10 http://www.sbri.fr/members/kenneth-knoblauch.html