If you queried an e-commerce API for a user's purchase history and received a result with a list attribute containing all their purchases, which transformer could you use to generate one feature per purchase?

• A. ListConcatenator
• B. ListExploder
• C. ListIndexer
• D. ListSorter

Answer: (B)

When you have a list attribute with multiple purchases and you need each purchase represented as its own feature, you want to split that list into separate features. The transformer that does this is ListExploder. It takes a feature containing a list and creates a new feature for every item in that list, preserving the rest of the attributes (like user ID) so you end up with one feature per purchase. This is perfect for turning an API’s array of purchases into a row-per-purchase dataset.

Other transformers don’t serve this exact purpose: ListConcatenator merges lists into a single list, not into multiple features; ListIndexer applies or creates indices within a list; ListSorter just orders elements within a list but keeps them in one feature.