Hi, @aleksandra_budnik!
I use the nested Rows plugin on handsontable v.7.0.3 and I was wondering, is there any chance to get the “parent” index by row? I need this because in cells function I have to get the sourceData and apply some logic depending on it.
Thanks in advance! 
There is no API method to get the indexes of the parent row. But here’s an approach that you can adapt https://jsfiddle.net/uh0sL2bw/4/ (based on the special className that is added to a TH element).
@aleksandra_budnik Thanks very much! I will defenetely play around with this one and try to see what’s the performance using it.