These days, you don't even need to look at the opposing lineup card to tell if the Pirates are going up against a left-handed pitcher. On most nights, if Neil Walker and Pedro Alvarez are out of the lineup, that usually means the opponents are going with a left-hander on the mound.
I've written many times about Walker and Alvarez being platoon players due to their struggles against lefties. The Pirates have been taking this route with Alvarez the last two years, although it hasn't always been a strict platoon, with the first baseman going up against some of the non-elite left-handers.