Nielsen (of TV ratings fame) has been selling this sort of data mining to grocers for decades. Decades ago I worked for a small regional chain and we based a l

Nielsen (of TV ratings fame) has been selling this sort of data mining to grocers for decades. Decades ago I worked for a small regional chain and we based a lot of decisions off that data - we could have never done it on our own. For any item in our stores we could get a list of other items that were commonly purchased together, for example. I'm sure it's even fancier nowadays.