I think the next article could be about group by. Like (only intuitively sofar...) A group by from A rows to B rows - is a map-reduce job - is an AxB linear t

I think the next article could be about group by. Like (only intuitively sofar...) A group by from A rows to B rows - is a map-reduce job - is an AxB linear transformation matrix from your linear algebra course - is...