Re: [Boost-users] Boost::Multi_array and reducing dimensions

From: Joey Mukherjee (joey_at_[hidden])
Date: 2008-06-26 14:43:19

Hi Ron,

This helped a great deal.  I have one follow on question:

Suppose this type of setup was within a function, is it possible to  
make OneDView the return value of this function?  In other words, I  
would like to:

array_type::const_array_view <1>::type OneDView;
OneDView = multi_array[myindices];
return OneDView;

In every dimensional case, could I construct my OneDView and save it  
to a variable so I have don't have to do the setup every time?  The  
reason I ask is I have this piece of code in a tight loop and it does  
take a bit of time.  Maybe there is an easier way to do it?   
Alternatively, I suppose I could copy the contents of the slice to  
another vector or array?.   Is there an easy C++/Boost way to do this?

When I compile the code above, I get a compiler error saying  
operator= is private as least that's what I think it is saying!

Joey

On Jun 18, 2008, at 11:51 AM, Ronald Garcia wrote:

> Hi Joey,
>
> I have looked at your self-contained example, so I get the gist of  
> what you're trying to do.  Rather than assigning to the array view,  
> you can assign to an indices object and build the view after the  
> fact.  Here's how to do the 2-dimensional case that you had  
> commented out:
>
>                      //This doesn't work, but I would love a  
> generic version of this:
>
>                      array_type::index_gen::gen_type<1,2>::type  
> myindices;
>                      if (desired_slice [0] == -1)
>                        myindices = indices [range ()][desired_slice  
> [1]];
>                          else
>                      if (desired_slice [1] == -1)
>                        myindices = indices [desired_slice [0]] 
> [range ()];
>
>                      array_type::const_array_view <1>::type OneDView
>                        = multi_array[myindices];
>
>                      ret_val = (OneDView [whichPosition]);
>
> HTH,
> ron
>
>
>
> On Jun 14, 2008, at 10:32 AM, Joey Mukherjee wrote:
>
>>
>> I am trying to use boost::multi_array and want to create a view  
>> where I am
>> lowering the number of dimensions, but I wish the dimension to be  
>> reduced
>> to be decided at runtime.
>>
>> I have a vector of integers and this vector size is the same as  
>> the number
>> of dimensions.  If the vector [1] value is -1, then the first  
>> dimension
>> will have all values (i.e. range ()), otherwise it will be a number
>> indicating what slice to use.
>>
>
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