Hi everybody,
I want to ask your help to explain what is going on with my following
code:
> mydata <- data.frame(y=rbinom(100, 1, 0.5), x1=rnorm(100),
x2=rnorm(100))
> glm.fit.method <-
function(model,data,...){glm(formula=model,data=data,family="binomial",.
..)}
> fit1 <- glm(y ~ x1 + x2, data=mydata, family=binomial())
> update(fit1, .~1)
Call: glm(formula = y ~ 1, family = binomial(), data = mydata)
Coefficients:
(Intercept)
-0.04001
Degrees of Freedom: 99 Total (i.e. Null); 99 Residual
Null Deviance: 138.6
Residual Deviance: 138.6 AIC: 140.6
> fit2 <- glm.fit.method(y ~ x1 + x2, data=mydata)
> update(fit2, .~1)
Error in as.data.frame.default(data, optional = TRUE) :
cannot coerce class '"function"' into a data.frame
One might expect that model 1 and model 2 are the same. So, it is
strange when this error occured. We can fix it easily by telling
"update" which data to evaluate:
> update(fit2, .~1, data=mydata)
Call: glm(formula = y ~ 1, family = "binomial", data = mydata)
Coefficients:
(Intercept)
-0.04001
Degrees of Freedom: 99 Total (i.e. Null); 99 Residual
Null Deviance: 138.6
Residual Deviance: 138.6 AIC: 140.6
I guest the problem may due to the fact that "update" requires
specifying which data is updated or the dataset named "data". fit1 and
fit2 just differ in a very small point:
> fit1$call
glm(formula = y ~ x1 + x2, family = binomial(), data = mydata)
> fit2$call
glm(formula = model, family = "binomial", data = data)
I am looking forward to your response,
Thanks,
Lam Phung Khanh
PhD student
Centre for Tropical Medicine
Oxford University Clinical Research Unit
190 Ben Ham Tu, Quan 5, Ho Chi Minh City
Vietnam
E-mail: la...@oucru.org
P/S: Detail of my current R version is
R version 2.13.0 (2011-04-13)
Platform: i386-pc-mingw32/i386 (32-bit)
locale:
[1] LC_COLLATE=English_United States.1252
[2] LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C
[5] LC_TIME=English_United States.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods
[7] base
loaded via a namespace (and not attached):
[1] tools_2.13.0
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