Re: [Boost-users] [multi_array] how to modify the dimension of an array?

From: Rupert Bruce (rupert_at_[hidden])
Date: 2008-05-30 16:55:50

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r0d wrote:
> Hello everybody,
> 
> i'm looking for the best way to modify the dimensions of an array. For
> example, i got this one:
> 
> boost::multi_array<int, 2> array ( boost::extents[3][3] );
> 
> and i want to change it in an array of 5 dimensions.
> 
> Now, what i'm doing is to create a new array of 5 dimensions and copying the
> first one into it, then delete the first one. But i'm sure that a more
> efficient way exists. No?

use resize() - see below

TEST(multi_array)
    {
    boost::multi_array<int, 2> myArray ( boost::extents[3][3] );

    int values = 0;
    for(boost::multi_array<int, 2>::index i = 0; i != 3; ++i)
        {
        for(boost::multi_array<int, 2>::index j = 0; j != 3; ++j)
            {
            myArray[i][j] = values++;
            }
        }

    // Verify values
    int verify1 = 0;
    for(boost::multi_array<int, 2>::index i = 0; i != 3; ++i)
        {
        for(boost::multi_array<int, 2>::index j = 0; j != 3; ++j)
            {
            CHECK_EQUAL(myArray[i][j],verify1++);
            }
        }
    myArray.resize(boost::extents[5][5]);

    //continue setting 'values' in the newly added array space
    for(boost::multi_array<int, 2>::index i = 3; i != 5; ++i)
        {
        for(boost::multi_array<int, 2>::index j = 3; j != 5; ++j)
            {
            myArray[i][j] = values++;
            }
        }

    //check the original data is still there
    int verify2 = 0;
    for(boost::multi_array<int, 2>::index i = 0; i != 3; ++i)
        {
        for(boost::multi_array<int, 2>::index j = 0; j != 3; ++j)
            {
            CHECK_EQUAL(myArray[i][j],verify2++);
            }
        }

    //check that the new array space has correct values
    for(boost::multi_array<int, 2>::index i = 3; i != 5; ++i)
        {
        for(boost::multi_array<int, 2>::index j = 3; j != 5; ++j)
            {
            CHECK_EQUAL(myArray[i][j],verify1++);
            }
        }

    }

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