Represents an ordered index based on data provided by a virtual source. The index can be used by BigDeedle virtual frames and series, without accessing all data from the data source.
The index only evaluates the full key collection when needed. Most of the actual
work is delegated to the
IVirtualVectorSource<'K> value passed in the constructor.
Signature: source:IVirtualVectorSource<'K> -> VirtualOrderedIndex<'K>
Returns the underlying source associated with the index