What is the change in Stock compensation between 2018 and 2019?
{"Deferred tax assets:     -- Receivables and inventory": {"December 27, 2019 ": 4468, "December 28, 2018": 3978}, "Deferred tax assets:     -- Accrued expenses": {"December 27, 2019 ": 170, "December 28, 2018": 1835}, "Deferred tax assets:     -- Self-insurance reserves": {"December 27, 2019 ": 1957, "December 28, 2018": 2050}, "Deferred tax assets:     -- Net operating loss carryforwards ": {"December 27, 2019 ": 1393, "December 28, 2018": 1749}, "Deferred tax assets:     -- Stock compensation": {"December 27, 2019 ": 1894, "December 28, 2018": 1670}, "Deferred tax assets:     -- Operating lease liabilities ": {"December 27, 2019 ": 37740, "December 28, 2018": "\u2014"}, "Deferred tax assets:     -- Other ": {"December 27, 2019 ": 612, "December 28, 2018": 803}, "Deferred tax assets:     -- Total deferred tax assets ": {"December 27, 2019 ": 48234, "December 28, 2018": 12085}, "Deferred tax liabilities:     -- Property & equipment ": {"December 27, 2019 ": -5218, "December 28, 2018": -3446}, "Deferred tax liabilities:     -- Intangible assets ": {"December 27, 2019 ": -15192, "December 28, 2018": -13197}, "Deferred tax liabilities:     -- Contingent earn-out liabilities ": {"December 27, 2019 ": -1526, "December 28, 2018": -3179}, "Deferred tax liabilities:     -- Prepaid expenses and other ": {"December 27, 2019 ": -1379, "December 28, 2018": -1052}, "Deferred tax liabilities:     -- Operating lease right-of-use assets ": {"December 27, 2019 ": -34895, "December 28, 2018": "\u2014"}, "Deferred tax liabilities:     -- Total deferred tax liabilities ": {"December 27, 2019 ": -58210, "December 28, 2018": -20874}, "Deferred tax liabilities:     -- Valuation allowance ": {"December 27, 2019 ": -907, "December 28, 2018": -812}, "Deferred tax liabilities:     -- Total net deferred tax liability": {"December 27, 2019 ": -10883, "December 28, 2018": -9601}}
stock_compensation_2019 = df["Deferred tax assets:     -- Stock compensation"]["December 27, 2019 "]
stock_compensation_2018 = df["Deferred tax assets:     -- Stock compensation"]["December 28, 2018"]
answer = stock_compensation_2019 - stock_compensation_2018