What was the percentage change in total purchase commitments between 2018 and 2019?
{"Less than 1 year": {"July 27, 2019": 4239, "July 28, 2018": 5407}, "1 to 3 years": {"July 27, 2019": 728, "July 28, 2018": 710}, "3 to 5 years": {"July 27, 2019": "\u2014", "July 28, 2018": 360}, "Total": {"July 27, 2019": 4967, "July 28, 2018": 6477}}
total_2019 = df["Total"]["July 27, 2019"]
total_2018 = df["Total"]["July 28, 2018"]
answer = (total_2019 - total_2018) / total_2018 * 100.0