On Dec 9, 2009, at 2:22 PM, Dr R.K.S. Hankin wrote:
Hi.
I am having difficulty creating a formula for use with glm()
I have a matrix of an unknown number of columns and wish to estimate a
coefficient for each column, and one for the each product of a column
with another column.
In the case of a five-column matrix this would be:
x <- matrix(rnorm(100),ncol=5)
colnames(x) <- letters[1:5]
z <- rnorm(20)
lm(z~ -1+(a+b+c+d+e)^2,data=data.frame(x))
Call:
lm(formula = z ~ -1 + (a + b + c + d + e)^2, data = data.frame(x))
Coefficients:
a b c d e a:b a:c a:d -0.30021 -0.21465 0.12208 0.06308 0.28806
0.34482 -1.00072 0.48218
a:e b:c b:d b:e c:d c:e d:e
0.28786 -0.46306 0.39844 0.04436 0.32236 -0.09210 -1.06625
This is what I want: five single terms (a-e) and 5*(5-1)/2=10 (a:b to
d:e) for the cross terms. If there were 6 columns I would want
(a+b+c+d+e+f)^2 and have 21 (=6+15) terms.
How do I create a formula that does this for an arbitrary number of
columns?
thanks
Robin
Robin,
Try this:
lm(z ~ (.)^2 - 1, data = data.frame(x))
See the Details section of ?formula, which describes the use of '.' to
refer to all columns not otherwise already in the formula.
HTH,
Marc Schwartz
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
