What was the change in purchased components between 2018 and 2019?
{"Purchased components": {"April 26, 2019": 8, "April 26,2018": 12}, "Finished goods": {"April 26, 2019": 123, "April 26,2018": 110}, "Inventories": {"April 26, 2019": 131, "April 26,2018": 122}}
purchased_components_april_26_2019 = df["Purchased components"]["April 26, 2019"]
purchased_components_april_26_2018 = df["Purchased components"]["April 26,2018"]
answer = purchased_components_april_26_2019 - purchased_components_april_26_2018