Required library edition: 
Required library file: dhtmlxgrid_group.js
group grid content by values of specified column
ind - {number} column index to group by
mask - {array} optional, array, each value of which is mapped to the related column. The possible values are:
title - will be used for group-key;
cspan - organize colspan with a sibling cell (the same as in cspan in header);
stat_total - calculates total of values for the group;
stat_max - calculates maximum value in the group;
stat_min - calculates minimum value in the group;
stat_average - calculates average value in the group;
stat_count - calculates count of records in the group.
//minimal parameters set. Group rows by second column
mygrid.groupBy(1);
//maximal parameters set
mygrid.groupBy(2,["#stat_max","#title","","#stat_total","","#cspan","#cspan","#cspan"]);
Note: this method is incompatible with enableSmartRendering, enablePaging and enableDistributedParsing methods
See also: collapseAllGroups, collapseGroup, expandAllGroups, expandGroup