‪Create Excel pivot tables in C#.NET, VB.NET, Java, C++, PHP and other, using EasyXLS Excel library! The pivot tables are reports in Excel that summarize worksheet data for a customized and clearer view over it. EasyXLS library allows you to create a pivot table in Excel, to set the data source and to arrange its data and fields into desired areas.
http://www.easyxls.com/manual/basics/excel-pivot-table.html

If not familiar with pivot tables in MS Excel or for technical related details, learn about Excel pivot tables.