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

From: Ronald Garcia (garcia_at_[hidden])
Date: 2008-06-16 10:17:24

Hi Joey,

I can't quite follow what you are trying to do below.  Could you boil  
it down to a small self-contained program that I can compile and run?

Thanks,
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.
>
> You can see in case 2 what I have tried and maybe what I am trying  
> to do.
> Case 3 and 4 I am hard coding the dimensions where I want all  
> values, which
> does work, but I'd like to get rid of the hard-codedness and make  
> this more
> generic.
>
> Furthermore, I have a one dimensional array of values which I am
> "converting" to a boost::multi_array so I can slice into it with  
> the views.
> I won't know the dimensions until I read the data.  Is there a  
> better more
> generic way of doing this?  Something like a pointer to a N- 
> dimensional
> structure where I can just use the view?
>
> Thanks in advance for any ideas!
>
> Joey
>
> Here is my code:
>
> {
>     double ret_val;
>     typedef boost::multi_array_types::index_range range;
>
>     const VariableInfo &vinfo = GetVariable (si._sensor);
>     SubSensorType local_subsensors (si._subsensors);
>     assert (local_subsensors.size () == vinfo._sizes.size ());
>     switch (vinfo._sizes.size ()) {
>         case 0  : ret_val = vals [0];
>                   break;
>         case 1  : { // one-d array
>                       ret_val = (vals [whichPosition]);
>                   }
>                   break;
>
> // Now we get into slices, find the subsensor element that has -1, and
> // create a slice along that dimension
>
>         case 2  : { // two-dimensional array
>           typedef boost::const_multi_array_ref <double, 2> array_type;
>           array_type::index_gen indices;
>
>           array_type multi_array (&(vals [0]), vinfo._sizes);
> /*
>
> This doesn't work!
>
>           array_type::const_array_view <1>::type OneDView;
>           if (local_subsensors [0] == -1)
>               OneDView = multi_array [indices [range ()]
>                                               [local_subsensors [1]]];
>               else
>           if (local_subsensors [1] == -1)
>               OneDView = multi_array [indices [local_subsensors [0]
>                                               [range ()]]];
>
>           ret_val = (OneDView [whichPosition]);
> */
>                   }
>                   break;
>         case 3  : { // three-dimensional array
>
>               typedef boost::const_multi_array_ref <double, 3>  
> array_type;
>               array_type::index_gen indices;
>
>               array_type multi_array (&(vals [0]), vinfo._sizes);
>               array_type::const_array_view <1>::type OneDView =
>                     multi_array [indices [local_subsensors [0]]
>                                          [local_subsensors [1]]
>                                          [range ()]];
>               ret_val = (OneDView [whichPosition]);
>                   }
>                   break;
>         case 4  : { // four-dimensional array
>               typedef boost::const_multi_array_ref <double, 4>  
> array_type;
>               array_type::index_gen indices;
>
>               array_type multi_array (&(vals [0]), vinfo._sizes);
>               array_type::const_array_view <1>::type OneDView =
>                     multi_array [indices [local_subsensors [0]]
>                                          [local_subsensors [1]]
>                                          [local_subsensors [2]]
>                                          [range ()]];
>
>               ret_val = (OneDView [whichPosition]);
>                   }
>                   break;
>         default : assert (vinfo._sizes.size () < 4);
>
>     }
>     return (ret_val);
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users