public static PivotTable<TRow, TColumn, TValue> ToPivot<TItem, TRow, TColumn, TValue>(
this IEnumerable<TItem> source,
Func<TItem, TRow> rowSelector,
Func<TItem, TColumn> colSelector,
Func<IEnumerable<TItem>, TValue> aggregatFunc
)
where TRow : IComparable, IEquatable<TRow>
where TColumn : IComparable, IEquatable<TColumn>
{
var dic = source
.GroupBy(rowSelector)
.ToDictionary(x => x.Key, x => x.GroupBy(colSelector).ToDictionary(y => y.Key, y => aggregatFunc(y)));
return PivotTable.Create(dic);
}