[MOAB-dev] Question about getting entities with tag data

[Jason Kraftcheck]

Paul Wilson wrote:
> Hi there,
> 
> I have been digging through the interface and I can't seem to find a 
> function that will return an MBRange of entities formed by matching a 
> single tag against a set of tag values.  As far as I can tell, 
> get_entities_by_type_and_tag will return an MBRange of entities formed 
> by matching N tags against N corresponding values, but will not match 1 
> tag against M values.
> 
> Is there such a function?  If not, is there a recommended way to resolve 
> this? 

You can call the existing function m times, passing the 
MBInterface::UNITE flag (or INTERSECT if that's what you want.)  Or pass 
in m copies of the tag handle.

> My first attempt was to get each entity one at a time, but that 
> is extremely slow.  Perhaps better to get the tag data for all possible 
> entities and then throw out the ones that are not needed?
> 

MOAB's search of tag values is O(n).  If you need something faster, 
you'll have to construct your own map or hash table from value to handle.

- jason