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27 lines
718 B
Markdown
27 lines
718 B
Markdown
# unionBy
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Creates an array of unique values, in order, from all given arrays using a provided mapping function to determine equality.
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## Signature
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```typescript
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function unionBy<T, U>(arr1: T[], arr2: T[], mapper: (item: T) => U): T[];
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```
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### Parameters
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- `arr1` (`T[]`): The first array.
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- `arr2` (`U[]`): The second array.
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- `mapper`: (`(item: T) => U`): The function to map array elements to comparison values.
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### Returns
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(`T[]`): A new array containing the union of unique elements from `arr1` and `arr2`, based on the values returned by the mapping function.
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## Examples
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```typescript
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unionBy([{ id: 1 }, { id: 2 }], [{ id: 2 }, { id: 3 }], x => x.id);
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// Returns [{ id: 1 }, { id: 2 }, { id: 3 }]
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```
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