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How to pick one object out of all objects with a specific set of attributes?

Posted on 2008-10-23
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Last Modified: 2012-05-05
An expert here wrote the function below for me. Right now, I think the code only counts the number of objects that have all the attributes that the reference object "findThisGroup" has. Unfortunately, it also needs to pick one of these objects at random and return an attribute of the chosen object to the calling function. Getting the attribute out of the object can be done using an existing member function called "GetPeerGroupID()".

My thoughts on how to do this: create a vector that pushes each matching object onto a second vector using the value of result. then simply pick one of those objects at random and get the PeerGroup attribute out of the object by calling GetPeerGroupID(). I just don't know how to do this.

I've tried my best to comment each line so that it's easy to follow. If you have any questions, feel free to email me (see my profile). Thanks a bunch!

Dan
int SelectPeerGroup(int AgeGroup, int CTorCountyID)//calling fcn passes two attributes the PeerGroupID that is returned must have AgeGroup index and location index.

{

	bool foundMatch = false;
 

	for(int numberOfTries = 1; !foundMatch; numberOfTries++)

	{

		CPeerGroup findThisGroup(-1);//initialized PeerGroup object with dummy ID

		findThisGroup.SetAgeGroup(AgeGroup);//gives Peergroup object AgeGroup and location attributes

		findThisGroup.SetCTorCountyID(CTorCountyID);

		cout	<< "Looking for... \n"

				<< "County: \n"	<< findThisGroup.GetCTorCountyID()    << ", " 

				<< "Age: \n"	<< findThisGroup.GetAgeGroup()    << endl;
 

		//std::find returns an iterator pointing to the located match

		//std::find is in #include <algorithm>

		

		std::vector<CPeerGroup>& v = get_vector(); // calls a function that returns a vector of all existing PeerGroup objects and Assigns to a reference type for use below.

		vector<CPeerGroup>::iterator result = v.begin();

		int count = 0; // count matches found

		while (result != v.end())

		{

			result = std::find(result, v.end(), findThisGroup);//i believe the find function returns the index of the matching object

			if (result != v.end()) 

			{

				++count;

				/*cout	<< "\t" << ++count << ": " 

						<< (*result).GetPeerGroupID() << ", " 

						<< (*result).GetCTorCountyID()    << ", " 

						<< (*result).GetAgeGroup()    << endl;*/

			}

			if (result != v.end())

			result++; // If found one, prepare to look for the next

		}

		if (count == 0) cout << "Didn't find any!" << endl << endl;

		foundMatch = (count > 0);

	}
 

	//int index = DiscreteUniformDeviate(0, count - 1);

	//v.GetPeerGroupID();

	return 0;

}

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Question by:ltdanp22
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9 Comments
 

Author Comment

by:ltdanp22
ID: 22783984
Second paragraph edited:
My thoughts on how to do this: push each matching object onto a second vector using the value of "result". Then pick one of those objects at random using existing function DiscreteUniformVariate(0, vector.siz()) and get the PeerGroup attribute out of the object by calling GetPeerGroupID(). I just don't know how to do this.
Also, please ignore the second to last line "v.GetPeerGroupID();" as v is not a peergroup object.
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LVL 31

Expert Comment

by:Zoppo
ID: 22784057
Hi ,

you could do it somehoe like this:

> std::vector<CPeerGroup> v_result;
> while (result != v.end())
> {
>  result = std::find(result, v.end(), findThisGroup);//i believe the find function returns the index of the matching object
>  if (result != v.end())
>  {
>   ++count;
>   /*cout  << "\t" << ++count << ": " 
>   << (*result).GetPeerGroupID() << ", " 
>   << (*result).GetCTorCountyID()    << ", " 
>   << (*result).GetAgeGroup()    << endl;*/
>// add the found item to 'v_result'
>    v_result.push_back( *result );
>// I put this line here since there's no need to do another 'if'
>    result++; // If found one, prepare to look for the next
>   }
>  }
>  ...
> // now get one random item
> int n = rand() % v_result.size();
> CPeerGroup randomItem = v_result[ n ];


Hope that helps,

ZOPPO
0
 

Author Comment

by:ltdanp22
ID: 22790374
Zoppo,
Looks perfect. However, when I run the code I get this error message:
error C2065: 'v_PeerGroup : undeclared identifier
The revised function with your changes incorporated is in the attached snippet.
The v_PeerGroup vector is declared in the function. Should it be declared somewhere else? The header file or the main function?
Daniel
0
 

Author Comment

by:ltdanp22
ID: 22790379
Whoops. Forgot the snippet...
int SelectPeerGroup(int AgeGroup, int CTorCountyID)//DP2

{

	bool foundMatch = false;
 

	for(int numberOfTries = 1; !foundMatch; numberOfTries++)

	{

		CPeerGroup findThisGroup(-1);

		findThisGroup.SetAgeGroup(AgeGroup);

		findThisGroup.SetCTorCountyID(CTorCountyID);

		cout	<< "Looking for... \n"

				<< "County: \n"	<< findThisGroup.GetCTorCountyID()    << ", " 

				<< "Age: \n"	<< findThisGroup.GetAgeGroup()    << endl;
 

		//std::find returns an iterator pointing to the located match

		//std::find is in #include <algorithm>

		

		std::vector<CPeerGroup>& v = get_vector(); // Assign to a reference type and use.

		vector<CPeerGroup>::iterator result = v.begin();

		vector<CPeerGroup> v_PeerGroup;

		int count = 0; // count matches found

		while (result != v.end())

		{

			result = std::find(result, v.end(), findThisGroup);

			if (result != v.end()) 

			{

				++count;

				cout	<< "\t" << ++count << ": " 

						<< (*result).GetPeerGroupID() << ", " 

						<< (*result).GetCTorCountyID()    << ", " 

						<< (*result).GetAgeGroup()    << endl;

			v_PeerGroup.push_back(*result);

			result++; // If found one, prepare to look for the next

			}

		}

		if (count == 0) cout << "Didn't find any!" << endl << endl;

		foundMatch = (count > 0);

	}

	int Index = DiscreteUniformDeviate(0, v_PeerGroup.size());

	CPeerGroup SelectedPeerGroup = v_PeerGroup[Index];

	int PeerGroupID = SelectedPeerGroup.GetPeerGroupID();	//v.GetPeerGroupID();

	return PeerGroupID;

}

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Author Comment

by:ltdanp22
ID: 22791352
One more question: is there any difference between vector.push() and vector.push_back()?
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Author Comment

by:ltdanp22
ID: 22791415
Scratch that last question. I just answered it for myself.
 
 
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LVL 31

Accepted Solution

by:
Zoppo earned 500 total points
ID: 22794488
Hi ltdanp22,

the problem with 'v_PeerGroup' is that you use it outside the scope where it's declared.

Just move this line
> vector<CPeerGroup> v_PeerGroup;
before this line
> for(int numberOfTries = 1; !foundMatch; numberOfTries++)

Zoppo
0
 

Author Comment

by:ltdanp22
ID: 22805457
Hi Zoppo,
Thanks! Seems to have worked. Can you explain to me why this is necessary so I know what not to do in the future?
Is it because v_PeerGroup is deleted for every iteration of the for loop?
Dan
0
 
LVL 31

Expert Comment

by:Zoppo
ID: 22810911
Hi,

this was needed since every variable instantiated on the stack is only available within it's execution scope. Such a scope is simply the code between '{' and '}'. So, anything you declare within a '{', '}' block can't be accessed outside of this block.

ZOPPO
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