---title: selectAtom---
Ref: https://github.com/pmndrs/jotai/issues/36
```jsfunction selectAtom<Value, Slice>( anAtom: Atom<Value>, selector: (v: Value) => Slice, equalityFn: (a: Slice, b: Slice) => boolean = Object.is): Atom<Slice>```
This function creates a derived atom whose value is a function of the original atom's value,determined by `selector.`The selector function runs whenever the original atom changes; it updates the derived atomonly if `equalityFn` reports that the derived value has changed.By default, `equalityFn` is reference equality, but you can supply your favorite deep-equalsfunction to stabilize the derived value where necessary.
## Examples
```jsconst defaultPerson = { name: { first: 'Jane', last: 'Doe', }, birth: { year: 2000, month: 'Jan', day: 1, time: { hour: 1, minute: 1, }, },}
// Original atom.const personAtom = atom(defaultPerson)
// Tracks person.name. Updated when person.name object changes, even// if neither name.first nor name.last actually change.const nameAtom = selectAtom(personAtom, (person) => person.name)
// Tracks person.birth. Updated when year, month, day, hour, or minute changes.// Use of deepEquals means that this atom doesn't update if birth field is// replaced with a new object containing the same data. E.g., if person is re-read// from a database.const birthAtom = selectAtom(personAtom, (person) => person.birth, deepEquals)```
## CodeSandbox
<CodeSandbox id="8czek" />