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[Solved] Duplicate finder

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  • G Offline
    G Offline
    giesbert
    wrote on 25 Jan 2011, 21:22 last edited by
    #25

    memcpy copies in memory and does not compare them.

    AFAIK, he wanted to search for duplicates, so hashes would be faster. YOu don't want to do a full compare for all files with all files....

    Nokia Certified Qt Specialist.
    Programming Is Like Sex: One mistake and you have to support it for the rest of your life. (Michael Sinz)

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    • I Offline
      I Offline
      ixSci
      wrote on 25 Jan 2011, 21:27 last edited by
      #26

      Gerolf, thank you for the function name correction.
      And yes, you are right about the question. I've misinterpreted OP goal :)

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      • A Offline
        A Offline
        alex.dadaev
        wrote on 28 Jan 2011, 10:19 last edited by
        #27

        How do you think, is it correct?
        @
        while(it.hasNext())
        {
        it.next();
        if(it.peekPrevious().key()==it.peekNext().key())
        std::cout<<it.peekPrevious().value()<<"="
        <<it.peekNext().value()<<std::endl;
        }
        @

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        • G Offline
          G Offline
          goetz
          wrote on 28 Jan 2011, 11:04 last edited by
          #28

          No it is not correct.

          It compares only adjacent entries in your container.

          If your container is a map (QMap or QHash) and you use insert() to populate it then you will get no duplicates at all, since every key occurs only once, hence the keys at different positions are all distinct.

          You must use insertMulti() and values() to get a list of all entries with the same hash value. Or use QMultiMap/QMultiHash with the before mentioned methods.

          http://www.catb.org/~esr/faqs/smart-questions.html

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          • A Offline
            A Offline
            alex.dadaev
            wrote on 28 Jan 2011, 11:25 last edited by
            #29

            Yes, you're right, thanks

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            • A Offline
              A Offline
              alex.dadaev
              wrote on 29 Jan 2011, 16:23 last edited by
              #30

              i can't understand why it's not working :(
              @
              while(it.hasNext())
              {
              it.next();
              if(it.key()==it.peekNext().key()) {
              std::cout << "i've got you" << std::endl;
              }
              }
              @

              PS: i've used insertMulti() to add item to hash, as you said

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              • A Offline
                A Offline
                alex.dadaev
                wrote on 29 Jan 2011, 16:39 last edited by
                #31

                maybe like this?
                @int compare_flag;

                while(it.hasNext())
                {
                    it.next();
                    compare_flag = QString::compare(it.key(),it.peekNext().key(),Qt::CaseSensitive);
                                   if(compare_flag==0) {
                        std::cout << "i've got you" << std::endl;
                    }
                }@
                
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                • G Offline
                  G Offline
                  goetz
                  wrote on 29 Jan 2011, 16:45 last edited by
                  #32

                  The keys in a (hash) map are always distinct. You will never find two identical keys so your comparison will never be true.

                  And even if you had identical keys in your container you would only find them if they are adjacent in the list.

                  But I'm going to have a kind of déjà-vu...

                  To make things clearer for us to understand: You do have a multi hash/multi map. What do you put in there and what do you expect to come out?

                  http://www.catb.org/~esr/faqs/smart-questions.html

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                  • A Offline
                    A Offline
                    alex.dadaev
                    wrote on 29 Jan 2011, 17:01 last edited by
                    #33

                    @QHash<QString,int> FilesHash;@
                    QString key is MD5
                    int value - just a number of file

                    on output i want to see the names of similar files

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                    • G Offline
                      G Offline
                      goetz
                      wrote on 29 Jan 2011, 17:15 last edited by
                      #34

                      Ok, let's make things clearer step by step. Seems that you should make yourself comfortable with the concepts of a map.

                      A map (QHash is one) stores values associated with keys. Every key only exists once in the map - I wrote that several times, let's prove it:

                      @
                      QHash<QString, int> myHash;
                      myHash.insert("abc", 2);
                      myHash.insert("def", 3);
                      myHash.insert("abc", 5);

                      qDebug() << "hash keys:" << myHash.keys();

                      QHash<QString, int> myMultiHash;
                      myMultiHash.insertMulti("abc", 2);
                      myMultiHash.insertMulti("def", 3);
                      myMultiHash.insertMulti("abc", 5);

                      qDebug() << "multi hash keys:" << myMultiHash.keys();
                      @

                      What will the output be?

                      What will happen if you compare every key with every other?

                      http://www.catb.org/~esr/faqs/smart-questions.html

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                      • A Offline
                        A Offline
                        alex.dadaev
                        wrote on 29 Jan 2011, 17:34 last edited by
                        #35

                        insertMulti allows you to store items with similar keys

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                        • A Offline
                          A Offline
                          alex.dadaev
                          wrote on 29 Jan 2011, 17:35 last edited by
                          #36

                          without overwriting them

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                          • A Offline
                            A Offline
                            alex.dadaev
                            wrote on 31 Jan 2011, 08:58 last edited by
                            #37

                            what do you think about it?
                            @
                            bool ok;
                            QHashIterator<QString,int> it(FilesHash);
                            QHashIterator<QString,int> begin(FilesHash);
                            QHashIterator<QString,int> end(FilesHash);
                            while(it.hasNext()) {
                            it.next();
                            begin = qLowerBound(FilesHash.begin(), FilesHash.end(), it.key());
                            end = qUpperBound(begin, FilesHash.end(), it.key());
                            iter = begin;
                            while(iter!=end) {
                            if(*i=*it) {
                            ok = true;
                            } else { ok = false; }
                            }
                            }
                            @

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                            • A Offline
                              A Offline
                              alex.dadaev
                              wrote on 31 Jan 2011, 10:18 last edited by
                              #38

                              why i cannot do like this?
                              @QHashIterator<QString,int> iter(FilesHash);

                              while(it.hasNext()) {
                                  it.next();
                                  iter = qBinaryFind(FilesHash.begin(), FilesHash.end(), it.key());
                              }@
                              
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                              • A Offline
                                A Offline
                                alex.dadaev
                                wrote on 2 Feb 2011, 08:01 last edited by
                                #39

                                please note that the problem has been solved :)

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                                • G Offline
                                  G Offline
                                  giesbert
                                  wrote on 2 Feb 2011, 08:06 last edited by
                                  #40

                                  you can do it on your own:
                                  go to your first post and click edit :-)
                                  and edit the title.

                                  Nokia Certified Qt Specialist.
                                  Programming Is Like Sex: One mistake and you have to support it for the rest of your life. (Michael Sinz)

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                                  29 Jan 2011, 17:15

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