# uniqBy

Returns a new array containing only the unique elements from the original array, based on the values returned by the `mapper` function.

## Signature

```typescript
function uniqBy<T, U>(arr: T[], mapper: (item: T) => U): T[];
```

### Parameters

- `arr` (`T[]`): The array to process.
- `mapper` (`(item: T) => U`): The function used to convert the array elements.

### Returns

(`T[]`): A new array containing only the unique elements from the original array, based on the values returned by the `mapper` function.

## Examples

```typescript
uniqBy([1.2, 1.5, 2.1, 3.2, 5.7, 5.3, 7.19], Math.floor);
// [1.2, 2.1, 3.2, 5.7, 7.19]
```

```typescript
const array = [
  { category: 'fruit', name: 'apple' },
  { category: 'fruit', name: 'banana' },
  { category: 'vegetable', name: 'carrot' },
];
uniqBy(array, item => item.category).length
// 2
```