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28 lines
679 B
Markdown
28 lines
679 B
Markdown
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# meanBy
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Calculates the average of an array of numbers when applying the `getValue` function to each element.
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If the array is empty, this function returns `NaN`.
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## Signature
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```typescript
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export function meanBy<T>(items: T[], getValue: (element: T) => number): number;
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```
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### Parameters
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- `items` (`T[]`): An array to calculate the average.
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- `getValue` (`(item: T) => number`): A function that selects a numeric value from each element.
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### Returns
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(`number`): The average of all the numbers as determined by the `getValue` function.
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## Examples
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```typescript
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meanBy([{ a: 1 }, { a: 2 }, { a: 3 }], x => x.a); // Returns: 2
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meanBy([], x => x.a); // Returns: NaN
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```
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