[R] identifying a column name correctly to use in a formula
Rui Barradas
rui1174 at sapo.pt
Thu Mar 1 04:24:02 CET 2012
Hello,
>
> I have a large matrix (SNPs) that I want to cycle over with logistic
> regression with interaction terms. I have made a loop but I am struggling
> to identify to the formula the name of the column in a way which is
> meaningful to the formula. It errors becasue it is not evaluated proporly.
> You have must first write the formula in full, using 'paste'.
>
Try
DF <- data.frame(Resp=rnorm(10), B=rnorm(10), C=rnorm(10),
Interaction=rnorm(10))
#DF
for(i in 2:3){
cname <- colnames(DF)[i]
#
# In 3 steps to be more readable
Regr <- paste(cname, "Interaction", sep="*")
fmlaText <- paste("Resp", Regr, sep="~")
# After step 2 it's already printable
print(fmlaText)
# Step 3: transform it into a formula object
fmla <- as.formula(fmlaText)
model1 <- glm(fmla, data=DF)
print(summary(model1))
}
You have must first write the formula in full, using 'paste'.
Hope this helps,
Rui Barradas
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