I stumbled across a mild glitch when trying to compare the
result of gam() fitting with the result of lm() fitting.
The following code demonstrates the problem:
library(gam)
x <- rep(1:10,10)
set.seed(42)
y <- rnorm(100)
fit1 <- lm(y~x)
fit2 <- gam(y~lo(x))
fit3 <- lm(y~factor(x))
print(anova(fit1,fit2)) # No worries.
print(anova(fit1,fit3)) # Likewise.
print(anova(fit2,fit3)) # Throws an error.
print(anova(fit3,fit2)) # ``Works'' but gives negative degrees of
freedom and sum of squares.
Is this evidence of a ``bug''? Or am I being terribly young and
naive to
expect anova() to work at all in such circumstances?
The error thrown is:
Error in anova.glmlist(list(object, ...), test = test) :
(list) object cannot be coerced to type 'double'
cheers,
Rolf Turner
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