[R] rms::ols & I(.) in formulas

[Setlhare Lekgatlhamang]

Try this
Lm(y~X + I(X^2)), data=dd) # this runs OLS regression and it worked for me

Hope it helps

Lexi

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Otto Kässi
Sent: Thursday, July 01, 2010 3:28 PM
To: r-help at r-project.org
Subject: [R] rms::ols & I(.) in formulas

Dear R-helpers,

To start I would like to thank Prof. Harrell for package rms. It is
one of the most useful packages for R that I have encountered.

Turning to my problem, I encountered a surprising problem when working
with rms::ols. It seems that insulating terms in a formula by using
I() to insulate terms in a formula seems to occasionally create a bug.
See the example below:
library(rms)
x <- rnorm(100)
y <- rnorm(100)
dd <- data.frame(cbind(x,y))
ols(y ~ x + I(x^2), data=dd)

ols() function gives the error:
Error in if (!length(fname) || !any(fname == zname)) { :
 missing value where TRUE/FALSE needed

Has anyone else encountered something similar? Is this a bug or does
this behavior have a reason?

There are of course trivial workarounds: one can either use poly(x, 2)
or save x^2 as a new column to dd, but trying to debug this was a
pain.

With kind regards,
Otto Kassi

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