Re: [Boost-users] [multi_array] How to specify degenerate at runtime?

Subject: Re: [Boost-users] [multi_array] How to specify degenerate at runtime?
From: Anton Daneyko (self_at_[hidden])
Date: 2012-02-29 12:28:51

I have got the reply to that question here:
http://stackoverflow.com/questions/8482445/how-to-specify-degenerate-dimension-of-boost-multi-array-at-runtime

On Tue, Dec 13, 2011 at 12:24 AM, Anton Daneyko <self_at_[hidden]> wrote:

> Greetings to Boosters,
>
> I have a 3D multi_array and I would like to make 2D slices using
> dimensions specified at runtime. I know the index of degenerate dimension
> and an index of slice, that I want to extract in that degenerate dimension.
> Currently the ugly workaround looks like that:
>     if (0 == degenerate_dimension)
>     {
>         Slice slice =
> input_array[boost::indices[slice_index][range()][range()]];
>     }
>     else if (1 == degenerate_dimension)
>     {
>         Slice slice =
> input_array[boost::indices[range()][slice_index][range()]];
>     }
>     else if (2 == degenerate_dimension)
>     {
>         Slice slice =
> input_array[boost::indices[range()][range()][slice_index]];
>     }
>
> Is there a more beautiful way to construct index_gen object?
> Something like that:
>     var slicer;
>     for(int i = 0; i < 3; ++i) {
>         if (degenerate_dimension == i)
>             slicer = boost::indices[slice_index];
>         else
>             slicer = boost::indices[range()];
>     }
>     Slice slice = input_array[slicer];
>
> It seems each subsequent call to boost::indices::operator[] returns a
> different type depending on the dimensionality, so there's no way to use a
> single variable, that can hold the temporary index_gen object.
>