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

From: Rupert Bruce (rupert_at_[hidden])
Date: 2008-05-31 14:03:14

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r0d wrote:
> 
> 
> everweb wrote:
> 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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>>
>>

> Thank you everweb,

> but that's not what i want to do. Surely i expained badly my problem (my
> english is too bad).

> I want to change the number of dimensions of the array. For example, i got
> an array:
> boost::multi_array<int, 2>
> and i want to change it in
> boost::multi_array<int, 5>

> Is it possible to di it easyly?

Ah, when you said "modify the dimensions of an array", I interpreted
that as "modify the size of the dimensions", not "modify the number of
dimensions" !
So you want to go from myArray[3][3] to myArray[3][3][3][3][3], not from
[3][3] to [5][5] ?
In my mind, that is such a dramatic change that I can't see a way to
"easily" implement it - which of the 5 dimensions should be copied from
the original 2 - always the first 2 ?
What if you meant the hypothetical redimension() function to go from
[3][3] to [n][3][n][3][n] instead of [3][3][n][n][n] ?

I'd say your copy, delete is the best way forward.
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