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how to remove repeat element in a list

tomchen

Hi 

I want to remove repeated element that in a list, but I can't find the related function for this.

I try to use hash table to solve it , but the order of this list will be changed

does any other function for this ??

ex:

                                                      change to 

aa= list("AA" "AA" "AA" "BB" "BB")  -----------------> aa = list("AA" "BB)

 

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  • jimka

    HI Derek, an interesting varient of removing duplciates from a list comes up when you slightly relax the meaning of duplicate.  For example, suppose you want to look at a list of strings, removing duplicates, but looking at the strings in a case independenty way. For exmaple, you might consider "AAA", "Aaa", and "aaa" to be duplicates.   Here is how you might do it.  First generalize SkxUniquify so that it can use a function other than equal to compare two elements.  Thereafter, use this generalized SkxUniquify to implement SkxRemoveDupStringsCi ...

    (defun SkxUniquify (data @key (cmp equal))
      (mapcon (lambda (data)
                (unless (exists item (cdr data)
                          (cmp item (car data)))
                  (ncons (car data))))
              data)) 

    (defun SkxRemoveDupStringsCi (strings)
      (SkxUniquify strings
                   ?cmp (lambda (a b)
                          (equal (lowerCase a)
                                 (lowerCase b))))) 

    (SkxRemoveDupStringsCi '("Aaa" "AAA" "AAA" "ABC" "abc" "aaa" "AAA")) 
    => ("abc" "AAA")

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  • jimka

    HI Derek, an interesting varient of removing duplciates from a list comes up when you slightly relax the meaning of duplicate.  For example, suppose you want to look at a list of strings, removing duplicates, but looking at the strings in a case independenty way. For exmaple, you might consider "AAA", "Aaa", and "aaa" to be duplicates.   Here is how you might do it.  First generalize SkxUniquify so that it can use a function other than equal to compare two elements.  Thereafter, use this generalized SkxUniquify to implement SkxRemoveDupStringsCi ...

    (defun SkxUniquify (data @key (cmp equal))
      (mapcon (lambda (data)
                (unless (exists item (cdr data)
                          (cmp item (car data)))
                  (ncons (car data))))
              data)) 

    (defun SkxRemoveDupStringsCi (strings)
      (SkxUniquify strings
                   ?cmp (lambda (a b)
                          (equal (lowerCase a)
                                 (lowerCase b))))) 

    (SkxRemoveDupStringsCi '("Aaa" "AAA" "AAA" "ABC" "abc" "aaa" "AAA")) 
    => ("abc" "AAA")

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