What is derived state?

Derived state is state that is computed from other state, rather than being stored separately.

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#A simple example:

You have a list of products:

And derived state is, for example, the filtered products:

You don't store filtered manually - you just say: "Take products, process it, and here's the result".

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#Why it's needed:

• No data duplication
• Everything is always current and in sync
• No need to update manually with every change

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#Where it's used:

• computed() in signals
• map()/combineLatest() in RxJS
• selectors in NgRx

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Conclusion: Derived state is "smart" state that doesn't live on its own, but automatically follows the underlying data. You don't manage it manually - it just "happens".