private static ValueMap Train(IExceptionContext ectx, BinaryLoader ldr)
{
Contracts.AssertValue(ectx);
ectx.AssertValue(ldr);
ectx.Assert(ldr.Schema.ColumnCount == 2);
// REVIEW: Should we allow term to be a vector of text (each term in the vector
// would map to the same value)?
ectx.Assert(ldr.Schema.GetColumnType(0).IsText);
var schema = ldr.Schema;
var typeValue = schema.GetColumnType(1);
// REVIEW: We should know the number of rows - use that info to set initial capacity.
var values = ValueMap.Create(typeValue);
using (var cursor = ldr.GetRowCursor(c => true))
values.Train(ectx, cursor, 0, 1);
return(values);
}