filterSequence: get the different arguments of the users for a specific
course.

removeReduplicatePart: reorganise list without reduplicate idPart in the
same idSession and keeps the original order
    
removeReduplicate: output the list which had removed the reduplication 

getCorrectPSDsequence: input the sequence which produced from Premium
Sequence function, output the sequence without reduplicate idPart and
has the correct duration.

averagePartLengthForACourse
gets the average length of session for a course

averageDurationForPart
get the average duration of the special part in a special course