[R] weird question about lm() and data.frame
Guojun Zhu
shmilylemon at yahoo.com
Fri May 5 07:17:37 CEST 2006
I am still battling with my project :(
I have a line like this
lm(month.model$next.ret~.,month.model,na.action=na.omit)
month.model is a data frame with lots of columns. One
of them is "Oth", a dummy variable. I checked
month.model, there are two rows with number 1 and
others are either 0 or NA. the two rows with Oth==1
have no NA. I have totally about 900 rows. But after
the regression, the Oth's coefficient is NA. I do not
understand.
Another issue is also about NA. I offen use something
like "model[model$Oth==1,]", but it will not only
gives rows with oth==1, but also gives some rows with
all item as NA. I then changed this into "
month.model[(month.model$Oth==1)&(!is.na(month.model$next.ret)),]"
and it gives the same result. Finally I change it
into
"
month.model[(month.model$Oth==1)&(!is.na(month.model$Oth)),]"
and it works. next.ret is a column for sure. Can
anyone explain this to me?
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