Surprising Symbolic Model Formula Evaluations

x <- 1:10
y <- runif(10)
lm(y ~ 1:x)

lm(y ~ x:1)

lm(y ~ 1*x)

lm(y ~ x*1)

I can't duplicate your examples
This is what I see

y ~ 1:x

y ~ 1:x

Please try again in a vanilla R session, and send a reproducible example.
vanilla means start R from the operating system command line with
R --vanilla

this prevents any of your initialization files from being loaded.  See
?Startup
for details.

On Fri, Oct 11, 2019 at 1:05 PM Emi Tanaka <dr.emi.tanaka at gmail.com>
wrote:

Hi,

I'm wondering about some logics behind the following simplifications:

y ~ 1:x simplifies to y ~ 1
y ~ x:1 simplifies to y ~ 1
y ~ x*1 simplifies to y ~ x
y ~ 1*x simplifies to y ~ 1

Mainly I would have expected y ~ 1:x to simplify to y ~ x and the cross
operator to be invariant to order.

I have some further surprising cases below that I'd also like to know

more

about but just above will also be great.

https://rpubs.com/emitanaka/unexpected-formula-eval

Best,

Emi

*Dr. Emi Tanaka* | Lecturer in Statistics

Faculty of Science, School of Mathematics and Statistics


Secretary, NSW Branch, Statistical Society of Australia
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