how to use the countby function from the underscore library in typescript

To use the countBy function from the Underscore library in TypeScript, you first need to install Underscore via npm:

index.ts
npm install underscore
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Then, you can import the countBy function in your TypeScript file, and use it as follows:

index.ts
import * as _ from 'underscore';

const myList = [1, 2, 3, 1, 2, 1, 3, 3, 2];
const grouped = _.countBy(myList);

console.log(grouped);
// Output: { "1": 3, "2": 3, "3": 3 }
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The countBy function takes an array and groups its elements by the result of calling the provided function on each element. In the example above, no function is provided, so the elements are grouped by their own values. The function returns an object that maps each group key to the number of elements in that group.

I hope this helps! Let me know if you have any more questions.