public Cursor(PerGroupTransformBase <TLabel, TScore, TState> parent, DataViewRowCursor input, DataViewRowCursor groupCursor, bool[] active)
: base(parent.Host)
{
Ch.AssertValue(parent);
// REVIEW: Try to see if we can relax this requirement in case there are no
// active columns from the input (that are not required for output computation).
Ch.AssertValue(input);
Ch.AssertValue(groupCursor);
Ch.AssertValue(active);
_parent = parent;
_input = input;
_groupCursor = groupCursor;
_active = active;
_state = _parent.InitializeState(_input);
var bindings = _parent.GetBindings();
_getters = _parent.CreateGetters(_state, iinfo => active[bindings.MapIinfoToCol(iinfo)]);
_newGroupInGroupCursorDel = RowCursorUtils.GetIsNewGroupDelegate(_groupCursor, bindings.GroupIndex);
_newGroupInInputCursorDel = RowCursorUtils.GetIsNewGroupDelegate(_input, bindings.GroupIndex);
_labelGetter = _parent.GetLabelGetter(_groupCursor);
_scoreGetter = _parent.GetScoreGetter(_groupCursor);
}