Re: map and set classes implemented with a tree having dynamic order statistics

Maxim Yegorushkin <>
Thu, 9 Oct 2008 02:16:50 -0700 (PDT)
On Oct 9, 5:56 am, DJ Dharme <> wrote:

On Oct 8, 7:20 pm, Maxim Yegorushkin <>

On Oct 8, 2:16 pm, DJ Dharme <> wrote:

On Oct 8, 5:17 pm, Maxim Yegorushkin <>

On Oct 8, 10:20 am, DJ Dharme <> wrote=


      Does anybody know about a solid implementation of a m=

ap or a set

with dynamic order statistics which allows the user to access a n=


by its Index in log(N) time. I have a problem of sorting a huge d=


set and showing it row by row. I have to quickly jump to a new
starting point on demand. If I use the std set class it takes so =


iterations to jump to a new location since we have to increment t=


iterators until we get the correct row no.

Can you not use a sorted vector? Accessing elements by key is
O(lg(N)), by index is O(1) and there is no memory overhead compared=



Thanks for the reply, yes I have tested this with vectors but failed
since I have to dynamically change (add, update, remove) the records.
The record count can grow up to few millions. And when the vector
starts to re-allocate memory the program hangs for some time.


In this case you can use std::deque<> to avoid paying for reallocating
and moving many elements.

Also I have to sort the records on each update. So if I
use a vector large amount of items will be moved back and forth due t=


insertions and removals.

To insert an element in a sorted vector or deque you do lower_bound
followed by insert. No need to sort again the whole container.


Thanks Max, I forgot to mention that I have used a binary search to
insert items into the sorted vector. I never knew that I can use
lower_bound for this.

Just a small question, according to the documents the iterators in the
deque are getting invalidated when we insert new items to it. I am
currently having a map of iterators with the primary key of the
records as the key. This allows me to directly find the iterators to
the records without iterating through the set to find the correct
record. I am giving a sample code to make my points clear.

#include <map>
#include <set>
#include <string>

struct keycomp
        bool operator()(const char* zLeft, const char* zRight)
                return strcmp(zLeft, zRight) < 0;


class TableRow

        std::string s_Key;
        void* p_Data;
        bool b_HasChanged;


class TableModel;

class TableRowComparator
        TableRowComparator(TableModel* pModel):p_Model(pModel){}

        bool operator()(TableRow* pLeft, TableRow* pRight)
                return p_Model->CompareRows(pLeft, pRight=



        TableModel* p_Model;


typedef std::set<TableRow*, TableRowComparator> TABLE_ROW_SET;
typedef std::map<const char*, TABLE_ROW_SET::iterator, keycomp>

class TableModel
        TableModel(): o_RowComparator(this), set_TableRows(o_RowC=




        // Compare rows according whatever the way the user wants
        bool CompareRows(TableRow* pLeft, TableRow* pRight)
                //Do whatever comparison here
                return pLeft->p_Data - pRight->p_Data =

< 0;


        // This method adds a record from the table control, if a=


exists for
        // the same key, it will update it with the new data
        void AddData(const char* zKey, void* pData)
                TABLE_ROW_ITR_MAP::iterator itrMap = ma=


                TableRow* pRow = NULL;

                if(itrMap != map_TableRowItrs.end)
                        TABLE_ROW_SET::iterator i=

trSet = itrMap->second;

                        pRow = *itrSet;

t); // Erase the existing row since


                 // new one may be inserted to a


                 // different place



                        pRow = new TableRow;
                        pRow->s_Key = zKey;

                pRow->p_Data = pData;
                pRow->b_HasChanged = true;




        // This method removes a record from the table control
        void RemoveData(const char* zKey)
                TABLE_ROW_ITR_MAP::iterator itrMap = ma=


                if(itrMap != map_TableRowItrs.end)
                        TABLE_ROW_SET::iterator i=

trSet = itrMap->second;

                        TableRow* pRow = *itrSe=






                        delete pRow;

        // This method needs to access the set items by its index=

 to show it

in a
        // virtual list control on the Front-End
        void* GetData(int iIndex)
                // How to make this fast?, this is my que=


                // I am currently doing a caching mechani=

sm which is not mentioned

                // if I have a set with dynamic order sta=

tistics this can be taken

in Log(N) time
                // instead of the N time

                if(iIndex < set_TableRows.count())
                        TABLE_ROW_SET::iterator i=

trSet = set_TableRows.begin();

                        for (int iRow = 0 ; iRo=

w < iIndex ; ++iRow, ++itrSet);

                        return (*itrSet)->p_Data;

                return NULL;

        TableRowComparator o_RowComparator;
        TABLE_ROW_SET set_TableRows;
        TABLE_ROW_ITR_MAP map_TableRowItrs;

Now I see that you container actually has three indexes:
1) TableRow::s_Key.
2) TableRow::p_Data.
3) array index

As the first step I would try getting rid of index 3. Most grid
controls allow associating user data (a pointer) with a cell. You
could associate a pointer to TableRow with a row in a grid. Another
way is that you could extract the key from the GUI row and use that
instead of index.

Next you could use boost::multi_index container which allows having
multiple indexes in the same container. This way you don't need to
maintain an additional map of iterators/pointers for every additional
index. The code is simpler, more robust and less memory waste.



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