Suppose you have a dataset stored in two different formats. The first one is an CSV file containing nine variables, and the other one is the XDF file containing the same variables. The following are the variable names:

• YEAR
• QUARTER
• MONTH
• DAY_OF_MONTH
• DAY_OF_WEEK
• ORIGIN
• DEST
• DEP_DELAY
• ARR_DELAY

The objective is to calculate mean departure delay for each combination of origin and destination airports. The required library for this recipe is RevoScaleR.