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Lodash _.uniqBy


lodash is a JavaScript library that provides a suite of utility functions with a focus on consistency, modularity, and performance. One of the functions within lodash is the _.uniqBy method, which serves to create an array with unique values that have been determined by a specific key or property.

The _.uniqBy method takes two arguments: the input array and a function that returns the value used to compare uniqueness. The function is used to generate an array of unique values using a specified property or key to determine uniqueness.

The method's first argument is the input array, and the second argument is an iteratee function that is applied to each element in the input array. The iteratee function is called with one argument, the current array element, and is expected to return the property or key value to be used in determining uniqueness.

If the second argument is not a function, then it is treated as a property name, which is used to create an iteratee function that returns the property value of the input array.

The _.uniqBy method uses a Map data structure to store unique elements, each element in the input array is iterated through and added to the Map object only if it is not already present. Finally, the method returns an array of unique elements from the Map object.

In terms of performance, _.uniqBy has a time complexity of O(N), which makes it relatively faster than similar methods that use nested loops, especially when dealing with large datasets.

Overall, the _.uniqBy method is a useful utility function that allows for easy creation of arrays with unique elements based on a specified key or property. The method's ability to be flexible and fast makes it a powerful tool for any JavaScript developer.