I am fairly new to machine learning and I am learning with a book.
So if I want to classify customers by their purchases, how would that look?
Age and sex would be single features, but what about the purchase history? 1 customer could have 10.000 or more purchases (each article is categorized: electronics, hardware, software, ...) some may only have 1000 or 100.
So my data should look like this
customerId | sex | age | purchases
-----------|------|-----|-----------
383848 | w | 35 | 1234, 49239
and not like this?
customerId | sex | age | purchase1 | purchase2 | purchase3
-----------|------|-----|-----------|-----------|----------
383848 | w | 35 | 1234 | 49239 | null
The examples I have done until now don't cover this - so any pointers are really appreciated.