Example of a non-injective retract induced homomorphism of fundamental groups

Question

When answering this question I used the fact that when we have a retract $r:X \rightarrow Y$ the induced homomorphism $r_\ast: \pi_1(X) \rightarrow \pi_1(Y)$ is surjective. I can recall how to prove this fact, but I can't seem to remember any examples where the induced map wasn't an isomorphism. So I was wondering if there are some fairly simple examples of retractions where the induced map is not injective.

Answer 1

Take $X$ and $Y=\{x\}$ with $x\in X$. Therefore the obivous map $r:X\to Y$ is continuous. So $r_*:\pi_1(X)\to\{e\}$ is surjective but, if $X$ is not simply connected, it isn't injective.