On Nov 6, 2013, at 10:40 AM, Tal Galili tal.gal...@gmail.com wrote:
Hello all,
I just noticed the following behavior of plot:
x - c(1,2,9)
plot(x ~ x) # this is just like doing:
plot(x)
# when maybe we would like it to give this:
plot(x ~ c(x))
# the same as:
plot(x ~ I(x))
I was
It probably happens because plot(formula) makes one call to terms(formula) to
analyze the formula. terms() says there is one variable in the formula,
the response, so plot(x~x) is the same a plot(seq_along(x), x).
If you give it plot(~x) , terms() also says there is one variable, but
no response,
Interestingly, fitting an LM with x on both sides gives a warning, and
then drops it from the RHS, leaving you with just an intercept:
lm(x~x,data=d)
Call:
lm(formula = x ~ x, data = d)
Coefficients:
(Intercept)
4
Warning messages:
1: In model.matrix.default(mt, mf, contrasts) :
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