Multiple slopes
You learned about model.matrix()
and its relationship to glm()
during the video. Now, you can "peek under the hood" of R and see how formulas work. The input to model.matrix()
is similar to formula inputs of lm()
and glm()
with one key difference: model.matrix()
does not have a left-hand side (e.g. y ~
), only the right-hand side (e.g., ~ x
).
For example, model.matrix( ~ x1)
or model.matrix( ~ x1 + x2)
both would be valid inputs. The output from model.matrix()
is called a prediction matrix because it is the prediction (or right-hand side) of a formula in R.
During this exercise, you will use model.matrix()
with 2 vectors: size
and count
.
First, build a simple formula that only includes size
.
Second, build a formula that includes both size
and count
.
This exercise is part of the course
Generalized Linear Models in R
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# Use model.matrix() with size
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