Array of vectors

This is a discussion on Array of vectors within the C++ Programming forums, part of the General Programming Boards category; Is it possible to have an array of vectors, or a vector of vectors? This would be in place of ...

  1. #1
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    Array of vectors

    Is it possible to have an array of vectors, or a vector of vectors?
    This would be in place of a 2d array.

  2. #2
    C++ Witch laserlight's Avatar
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    Yes.
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    I tried creating it like this but it doesn't work. What is the proper way of creating one dynamically?
    Code:
    k = vars.NumScan;
    
    vector <long int> vectAWords[k];
    Last edited by earth_angel; 07-12-2005 at 07:15 AM.

  4. #4
    Registered User mitakeet's Avatar
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    Here is an example of a 3d array of vectors emulating a matrix using references to avoid copying:

    Code:
    #include <iostream>
    #include <vector>
    
    using namespace std;
    
    int main(){
        int x = 3, y = 3, z = 3;
        int i, j, k;
        vector < vector < vector < int > > > matrix3d;
    
        matrix3d.resize(x);
        for (i=0; i<x; i++){
            vector < vector < int > > &vect2d = matrix3d[i];
            vect2d.resize(y);
            for (j=0; j<y; j++){
                vector < int > &vectLastD = vect2d[j];
                vectLastD.resize(z);
                for (k=0; k<z; k++){
                    vectLastD[k] = i+j+k;
                }
            }
        }
    
        for (i=0; i<x; i++){
            for (j=0; j<y; j++){
                for (k=0; k<z; k++){
                    cout << matrix3d[i][j][k] << ' ';
                }
                cout << endl;
            }
            cout << endl;
        }
    
        return 0;
    }

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  5. #5
    C++ Witch laserlight's Avatar
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    What is the proper way of creating one dynamically?
    The usual, e.g.
    Code:
    std::vector<int>* foo;
    foo = new std::vector<int>[size];
    //use foo for some devious purpose
    delete[] foo;
    But yeah, a vector of vectors might be better.
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  6. #6
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    OK.
    That's intense, took me a while to figure out all the counters and such.

    Looking at that example, I tried this code :
    Code:
    int TempWord = 0;
    
    	long int *AWordMtx;
    
    	AWords = new long int[vars.NumScan];
    
    	for (j=0; j< vars.NumScan; j++)
    	{
    		vector <long int> AWordLine = AWordMtx[j];
    
    		for( i=0; i< vars.vectParmSelected.size(); i++)
    		{
    			TempValue = i+2;
    
    			if(TempValue > 1)
    				AWordMtx[i].AWordLine.push_back(TempWord);
    
    		}
    	}
    I know it's wrong, how would it be fixed?

  7. #7
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    > The usual, e.g.

    Oh, It's always easier then I think. I'll give it a shot

  8. #8
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    There's no reason to dynamically allocate an array of vectors. Try giving a vector of vectors a shot.

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