What was the change in Share-based compensation expense between 2018 and 2019?
{"ASSETS -- Allowance for doubtful accounts and returns .": {"July 27, 2019": 127, "July 28, 2018": 285}, "ASSETS -- Sales-type and direct-financing leases": {"July 27, 2019": 176, "July 28, 2018": 171}, "ASSETS -- Inventory write-downs and capitalization": {"July 27, 2019": 409, "July 28, 2018": 289}, "ASSETS -- Investment provisions .": {"July 27, 2019": "\u2014", "July 28, 2018": 54}, "ASSETS -- IPR&D, goodwill, and purchased intangible assets": {"July 27, 2019": 1427, "July 28, 2018": 63}, "ASSETS -- Deferred revenue .": {"July 27, 2019": 1150, "July 28, 2018": 1584}, "ASSETS -- Credits and net operating loss carryforwards .": {"July 27, 2019": 1241, "July 28, 2018": 1087}, "ASSETS -- Share-based compensation expense": {"July 27, 2019": 164, "July 28, 2018": 190}, "ASSETS -- Accrued compensation": {"July 27, 2019": 342, "July 28, 2018": 370}, "ASSETS -- Other": {"July 27, 2019": 419, "July 28, 2018": 408}, "ASSETS -- Gross deferred tax assets": {"July 27, 2019": 5455, "July 28, 2018": 4501}, "ASSETS -- Valuation allowance": {"July 27, 2019": -457, "July 28, 2018": -374}, "ASSETS -- Total deferred tax assets .": {"July 27, 2019": 4998, "July 28, 2018": 4127}, "LIABILITIES -- Purchased intangible assets .": {"July 27, 2019": -705, "July 28, 2018": -753}, "LIABILITIES -- Depreciation .": {"July 27, 2019": -141, "July 28, 2018": -118}, "LIABILITIES -- Unrealized gains on investments .": {"July 27, 2019": -70, "July 28, 2018": -33}, "LIABILITIES -- Other": {"July 27, 2019": -112, "July 28, 2018": -145}, "LIABILITIES -- Total deferred tax liabilities": {"July 27, 2019": -1028, "July 28, 2018": -1049}, "LIABILITIES -- Total net deferred tax assets": {"July 27, 2019": 3970, "July 28, 2018": 3078}}
share_based_compensation_expense_2019 = df["ASSETS -- Share-based compensation expense"]["July 27, 2019"]
share_based_compensation_expense_2018 = df["ASSETS -- Share-based compensation expense"]["July 28, 2018"]
answer = share_based_compensation_expense_2019 - share_based_compensation_expense_2018