And this is one of many reasons why Redux encourages you to normalize your state - you can retrieve any item with a couple simple direct lookups (such as `state.entities[type].byId[id]`), rather than mapping over an array comparing item IDs. Granted, O(n) array loops aren't likely to be a real perf issue until you hit fairly large values of N.

As you said, I covered this in the "Structuring Reducers - Normalizing State Shape" and "Immutable Update Patterns" sections of the docs: http://redux.js.org/docs/recipes/reducers/NormalizingStateSh... and http://redux.js.org/docs/recipes/reducers/ImmutableUpdatePat... .