Answer by Shiroo for React + Redux - architectural Apis approach

You can use reselect (library) and you could get correct result thanks to that by merging properties in selector. https://github.com/reduxjs/reselect

It is well normalized state so there is no point in denormalizing it.

So firstly you would get all elements from normalized state and then get all possible results from second API. Iterate through first elements and filter out answers from 2nd API where parentId doesnt equal to id.