XEROF

Build 5.0.0.20 of xlsgen adds read and write support for the following functions :

GROUPBY : allows you to create a summary of your data via a formula. It supports grouping along one axis and aggregating the associated values. For instance, if you had a table of sales data, you might generate a summary of sales by year. Syntax : =GROUPBY(row_fields,values,function,[field_headers],[total_depth],[sort_order],[filter_array])
PIVOTBY : allows you to group, aggregate, sort, and filter data based on the row and column fields that you specify. Syntax : =PIVOTBY(row_fields,col_fields,values,function,[field_headers],[row_total_depth],[row_sort_order],[col_total_depth],[col_sort_order],[filter_array])
PERCENTOF : returns the percentage that a subset makes up of a given data set. Syntax : =PERCENTOF(data_subset,data_all)

Functions are available from Microsoft in Excel 365. In beta at the time of writing.