t4, Common Lisp - rextester

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;gnu clisp  2.49.60
#|Про каждого студента известная следующая информация: 
    какой предмет сдавал, каковы были результаты (оценки от 2 до 5), когда происходил экзамен или пересдача. 
Написать функцию, которая по заданным предметам упорядочивает список студентов по возрастанию количества пересдач.
|#

(defun slice-subject (students subject)
    (loop for s in students
         if (and (string= (second s) subject) (string= (fifth s) "retaking"))
          collect s
     )   
 )

(defun sort-retakes (students subject)
    (setf students (slice-subject students subject))
    (let (name))
    (let (count))
    (let (el))
    (loop while (not (null students))
          do (setf name (first (first students)))
          do (print (first (first students)))
          do (setf count (count-if #'(string= (first (first students)) name) students))
          do (setf students (remove-if (string= (first (first students)) name) students))
          do (setf el (list name count))
         collect el
     )
    
    )

(let (students))
(setf students '(("Magalish" "English" 5 (20 5 2020) "exam") ("Magalish" "Algorithms" 2 (20 5 2020) "exam") ("Magalish" "Algorithms" 53 (20 10 2020) "retaking")
                  ("Magalish" "Modeling" 2 (20 6 2020) "exam") ("Magalish" "Modeling" 4 (20 6 2020) "retaking") 
                   ("Skopina" "Modeling" 2 (20 6 2020) "exam") ("Skopina" "Modeling" 4 (20 6 2020) "retaking") ("Skopina" "Modeling" 4 (23 6 2020) "retaking") ))

(print (sort-retakes students "Modeling"))

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Absolute running time: 0.17 sec, cpu time: 0.02 sec, memory peak: 9 Mb, absolute service time: 0,28 sec