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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 Andrew, I agree that the fastest way to remove duplicates is using a hash table.  But a warning should sit above such a function as CCFuniqueInOrder.  One must be sure that the unbound symbol is not in the list being examined.  The unbound symbol is indeed likely to appear in the list if your application is operating on SKILL code.  E.g., if you are trying to find all the symbols in your SKILL code for the purpose of examining function prefixes etc.

    Another limitation of hash tables is that not all SKILL data types are valid hash keys.  Three types come to mind quickly.  CDF objects (such as returned from cdfGetInstCDF), PCRE compiled expressions (such as returned from pcreCompile), and hash tables themselves.  If you attempt to use CCFuniqueInOrder to remove duplicates from a given list of hash tables, i.e., a list of hash tables which might contain the same hash table more than once, then uniq[elem] will trigger an error.

    For example:

     (let ((x (makeTable 'x)) (y (makeTable 'y))) (CCFuniqueInOrder (list x x y y)))
    *Error* assoc hash: given user type is not supported in assoc tables - table:x
    <<< Stack Trace >>>
    uniq[elem]
    boundp(uniq[elem])
    !boundp(uniq[elem])
    (!boundp(uniq[elem]) && (uniq[elem] = t))
    setof(elem lst (!boundp(&) && (uniq[elem] = t)))
    let(((uniq makeTable(&))) setof(elem lst (!& && (uniq[elem] = t))))
    CCFuniqueInOrder(list(x x y y))
    let(((x makeTable(&)) (y makeTable(&))) CCFuniqueInOrder(list(x x y y)))

     

    Admittedly this case is exremely rare. Most SKILL users will never need to worry about such extreme corner case.

    Regards,

    Jim. 

Reply
  • jimka

    Hi Andrew, I agree that the fastest way to remove duplicates is using a hash table.  But a warning should sit above such a function as CCFuniqueInOrder.  One must be sure that the unbound symbol is not in the list being examined.  The unbound symbol is indeed likely to appear in the list if your application is operating on SKILL code.  E.g., if you are trying to find all the symbols in your SKILL code for the purpose of examining function prefixes etc.

    Another limitation of hash tables is that not all SKILL data types are valid hash keys.  Three types come to mind quickly.  CDF objects (such as returned from cdfGetInstCDF), PCRE compiled expressions (such as returned from pcreCompile), and hash tables themselves.  If you attempt to use CCFuniqueInOrder to remove duplicates from a given list of hash tables, i.e., a list of hash tables which might contain the same hash table more than once, then uniq[elem] will trigger an error.

    For example:

     (let ((x (makeTable 'x)) (y (makeTable 'y))) (CCFuniqueInOrder (list x x y y)))
    *Error* assoc hash: given user type is not supported in assoc tables - table:x
    <<< Stack Trace >>>
    uniq[elem]
    boundp(uniq[elem])
    !boundp(uniq[elem])
    (!boundp(uniq[elem]) && (uniq[elem] = t))
    setof(elem lst (!boundp(&) && (uniq[elem] = t)))
    let(((uniq makeTable(&))) setof(elem lst (!& && (uniq[elem] = t))))
    CCFuniqueInOrder(list(x x y y))
    let(((x makeTable(&)) (y makeTable(&))) CCFuniqueInOrder(list(x x y y)))

     

    Admittedly this case is exremely rare. Most SKILL users will never need to worry about such extreme corner case.

    Regards,

    Jim. 

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