What was the difference in Weighted Average Grant Date Fair Value between Vested and Forfeited shares?
{"Nonvested at December 31, 2018": {"Number of Shares": 213337.0, "Weighted Average Grant Date Fair Value": 20.21}, "Vested": {"Number of Shares": -106610.0, "Weighted Average Grant Date Fair Value": 20.17}, "Forfeited": {"Number of Shares": -13885.0, "Weighted Average Grant Date Fair Value": 20.64}, "Nonvested at December 31, 2019": {"Number of Shares": 92842.0, "Weighted Average Grant Date Fair Value": 20.13}}
forfeited_weighted_average_grant_date_fair_value = df["Forfeited"]["Weighted Average Grant Date Fair Value"]
vested_weighted_average_grant_date_fair_value = df["Vested"]["Weighted Average Grant Date Fair Value"]
answer = forfeited_weighted_average_grant_date_fair_value - vested_weighted_average_grant_date_fair_value