The formula is just like this. I don't quite understand the usage of the notion "/". It seems that "/" usually be used in dummy variables. But I am not sure about its usage.
lm(y~x/z,data = data.frame(x = rnorm(6), y = rnorm(6), z = rep(0:1,each=3)))
lm(y ~ x/z, data)
is just a shortcut for lm(y ~ x + x:z, data)
These two give the same results:
lm(mpg ~ disp/hp,data = mtcars)
Call:
lm(formula = mpg ~ disp/hp, data = df)
Coefficients:
(Intercept) disp disp:hp
2.932e+01 -3.751e-02 -1.433e-05
lm(mpg ~ disp + disp:hp, data = mtcars)
Call:
lm(formula = mpg ~ disp + disp:hp, data = mtcars)
Coefficients:
(Intercept) disp disp:hp
2.932e+01 -3.751e-02 -1.433e-05
So, what your doing is modelling mpg
based on disp
alone and on an interaction between disp
and hp
.
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