func setOrder(_ fieldlist: String)

Function setOrder() sets order of records by some field or list of fields.
The function does not change a file, it re-orders records in a memory.
One function accepts a string with fields delimited by comma, another function accepts an array.
To return the original order of records - call unserOrder().
function descendingMode() set either ascending or descending order.

func setOrderA(_ array: [String])
func unsetOrder()
func descendingMode(_ descending: Bool)

{
    // your code
    dbf.setOrder("FIRSTNAME,LASTNAME")
    dbf.descendingMode(true)
    dbf.setOrderA( ["FIRSTNAME", "LASTNAME"] )
    // your code
    dbf.unsetOrder()
}