R - Create a dataframe that lists down average spend for each day : I have the following data frame, listing the spends for each category for each day

    Dataframe: actualSpends
    Date         Category  Spend ($) 
    2017/01/01   Apple     10
    2017/01/02   Apple     12
    2017/01/03   Apple     8 
    2017/01/01   Banana    13
    2017/01/02   Banana    15
    2017/01/03   Banana    7


I want to create a new data frame that will list down the average amount spend for each category, for each day of the month. 
(e.g. On the 3rd of the month, the average spend of all days that have passed in the month, from the 1st to 31st of each month. )