22 lines
777 B
Markdown
22 lines
777 B
Markdown
---
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title: symmetricDifferenceBy
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tags: array,intermediate
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---
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Returns the symmetric difference between two arrays, after applying the provided function to each array element of both.
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- Create a `Set` by applying `fn` to each array's elements, then use `Array.prototype.filter()` on each of them to only keep values not contained in the other.
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```js
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const symmetricDifferenceBy = (a, b, fn) => {
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const sA = new Set(a.map(v => fn(v))),
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sB = new Set(b.map(v => fn(v)));
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return [...a.filter(x => !sB.has(fn(x))), ...b.filter(x => !sA.has(fn(x)))];
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};
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```
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```js
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symmetricDifferenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [ 1.2, 3.4 ]
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symmetricDifferenceBy([{ id: 1 }, { id: 2 }, { id: 3 }], [{ id: 1 }, { id: 2 }, { id: 4 }], i => i.id) // [{ id: 3 }, { id: 4 }]
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```
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