[R] ols function in rms package

[Mark Seeto]

Hello,

I have a couple of questions about the ols function in Frank Harrell's rms
package.

Is there any way to specify variables by their column number in the data
frame rather than by the variable name?

For example,

library(rms)
x1 <- rnorm(100, 0, 1)
x2 <- rnorm(100, 0, 1)
x3 <- rnorm(100, 0, 1)
y <- x2 + x3 + rnorm(100, 0, 5)
d <- data.frame(x1, x2, x3, y)
rm(x1, x2, x3, y)
lm(y ~ d[,2] + d[,3], data = d)  # This works
ols(y ~ d[,2] + d[,3], data = d) # Gives error
Error in if (!length(fname) || !any(fname == zname)) { :
  missing value where TRUE/FALSE needed

However, this works:
ols(y ~ x2 + d[,3], data = d)

The reason I want to do this is to program variable selection for
bootstrap model validation.

A related question: does ols allow "y ~ ." notation?

lm(y ~ ., data = d[, 2:4])  # This works
ols(y ~ ., data = d[, 2:4]) # Gives error
Error in terms.formula(formula) : '.' in formula and no 'data' argument

Thanks for any help you can give.

Regards,
Mark
-- 
Mark Seeto
Statistician

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