last returns the last value found within the specified sequence as defined by last([Group by this field], "identifier", [Sort by this field], [Return this field]).
last([Project ID], "ProjectLast", [Todo Completed At], [Todo Name])
would return the last completed Todo Name for each distinct Project ID.
first returns the first value found within the specified sequence as defined by first([Group by this field], "identifier", [Sort by this field], [Return this field]).
first([Project ID], "ProjectLast", [Todo Completed At], [Todo Name])
would return the first completed Todo Name for each distinct Project ID.