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HTML

              
                
              
            
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CSS

              
                
              
            
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JS

              
                /*!
 * Group items from an array together by some criteria or value.
 * (c) 2021 Tom Bremmer (https://tbremer.com/) and Chris Ferdinandi (https://gomakethings.com), MIT License,
 * @param  {Array}           arr      The array to group items from
 * @param  {String|Function} criteria The criteria to group by
 * @return {Object}                   The grouped object
 */
function groupBy (arr, criteria) {
	return arr.reduce(function (obj, item) {

		// Check if the criteria is a function to run on the item or a property of it
		let key = typeof criteria === 'function' ? criteria(item) : item[criteria];

		// If the key doesn't exist yet, create it
		if (!Object.prototype.hasOwnProperty.call(obj, key)) {
			obj[key] = [];
		}

		// Push the value to the object
		obj[key].push(item);

		// Return the object to the next item in the loop
		return obj;

	}, {});
}


let nums = [6.1, 4.2, 6.3];
let words = ['one', 'two', 'three'];

let groupedNums = groupBy(nums, Math.floor);
let groupedWords = groupBy(words, 'length');

console.log(groupedNums);
console.log(groupedWords);
              
            
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999px

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