Currently when sampling is used to generate the data points, the DataItem property of the DataPoint is null and there is no way to find out which data items have been used to generate the data point. A new property can be introduced (DataItems) which can contain the data items in mind.

Decline reason: This item is duplicate of the following one:
http://feedback.telerik.com/Project/143/Feedback/Details/113364-chartview-expose-the-data-items-when-sampling-is-used