How to plot a comparisson of two fixed categorical values for linear regression of another continuous variable

Question

So I want to plot this:

lmfit = lm (y ~ a + b)

but, \"b\" only has the values of zero and one. So, I want to plot two separate regre

Answer 1

Unless I've misunderstood the question, all you have to do is run abline again but on a model without the b term.

abline(lm(y~a),col="red",lwd=2)