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

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 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 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 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@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users