Variable names in model formula
At 10:37 PM 5/1/00 -0400, E. S. Venkatraman wrote:
I have the following problem. I have survival data (time, status) along
with several covariates (X1, X2,..., Xn). I want to fit a Cox model for
each of the covariate (univariately) and obtain the fitted probability of
survival at a fixed time point t0 and covariate value Xi0. I tried to do
this in a for loop where the index is the variable name as follows
covnames <- names(...)
for (covi in covnames) {
survout <- coxph(Surv(time,status) ~ covi, data = dataname)
print(summary(survfit(survout,newdata),t0))
}
You could try
covnames <- names(...)
form <- Surv(time, status) ~ dummy
for(nam in covnames) {
form[[3]] <- as.name(nam)
survout <- coxph(form, data = dataname)
print(summary(survfit(survout, newdata), t0))
}
Unfortunately "covi" is being treated as the variable name instead of being evaluated and the coxph call gives an error. None of as.character, eval, substitute (at least the way I called them) worked. How does one pass on variable names to model formula?
The above way is one. A slightly more direct way would be to use some
column of the data frame on the right hand side:
for (i in 1:5) {
survout <- coxph(Surv(time, status) ~ dataname[, i], dataname)
.....
}
There is a distinction between character strings and names.
Thanks, Venkat ----------------------------------------------------------------------- E. S. Venkatraman, Ph.D. Phone: (212) 639-8520 Fax: (212) 717-3137 Assistant Attending Member Memorial Sloan-Kettering Cancer Center ----------------------------------------------------------------------- -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
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