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Lodash _.invertBy


The lodash _.invertBy method is a powerful utility function provided by the popular JavaScript library, Lodash. This function is used to create an object composed of keys generated from the results of running each element of a collection through a function that produces a corresponding key, with the corresponding value being the array of elements responsible for generating the key.

Here is the syntax for the _.invertBy method:

_.invertBy(collection, iteratee)

The first argument, collection, is the array or object to be inverted. The second argument, iteratee, is the function that is called with each element in the collection. The value returned by iteratee will be used as the key for the created object.

The _.invertBy method takes each element of the input collection and applies the iteratee function to it. The result of the function is used as a key in a new object, and the element that produced that key is stored in an array at that key. If multiple elements produce the same key, they are all included in the array for that key.

Here is an example of how to use the _.invertBy function:

const numbers = {
  one: 1,
  two: 2,
  three: 3,

const result = _.invertBy(numbers, (number) => {
  if (number % 2 === 0) {
    return 'even';
  return 'odd';

// Output: { odd: [ 'one', 'three' ], even: [ 'two' ] }

In this example, the input collection is an object numbers with key/value pairs representing numbers. The iteratee function checks whether each number is even or odd and returns the corresponding key. The .invertBy() method creates an object in which the keys are 'odd' and 'even', with the values being arrays of corresponding numbers.

Overall, the _.invertBy method is a useful utility function for quickly and easily inverting an object or array and grouping items based on their properties.