In my current code, I do not get the desired output because the value of the key obj[2] gets updated to 2.4 since the value is a number and not an array.
Is there a simple way to store the property values as an array and push these elements onto the array? (see instructions in code)
// Create a function groupBy that accepts an array and a callback, and returns an object. groupBy will iterate through the array and perform the callback on each element.
// Each return value from the callback will be saved as a key on the object.
// The value associated with each key will be an array consisting of all the elements
//that resulted in that return value when passed into the callback.
function groupBy(array, callback) {
const obj = {};
array.forEach((el) => {
const evaluated = callback(el);
obj[evaluated] = el
});
return obj
}
//current output : {1: 1.3, 2: 2.4}
const decimals = [1.3, 2.1, 2.4];
const floored = function(num) {
return Math.floor(num);
};
console.log(groupBy(decimals, floored)); // should log: { 1: [1.3], 2: [2.1, 2.4] }CodePudding user response：
Initialize the obj[evaluated] if it's undefined to an empty array, and push the item to the array.
If supported you can use the Logical nullish assignment (??=) to assign an empty array to obj[evaluated] if it's null or undefined:
function groupBy(array, callback) {
const obj = {};
array.forEach((el) => {
const evaluated = callback(el);
(obj[evaluated] ??= []).push(el);
});
return obj
}
const decimals = [1.3, 2.1, 2.4];
const floored = function(num) {
return Math.floor(num);
};
console.log(groupBy(decimals, floored)); // should log: { 1: [1.3], 2: [2.1, 2.4] }