JavaScript: Reduce a given Array-like into a value hash

JavaScript fundamental (ES6 Syntax): Exercise-124 with Solution

Reduce Array-Like to Hash Map

Write a JavaScript program to reduce a given Array-like into a value hash (keyed data store).

Note: Given an Iterable or Array-like structure, call Array.prototype.reduce.call() on the provided object to step over it and return an Object, keyed by the reference value.

• Given an iterable object or array-like structure, call Array.prototype.reduce.call() on the provided object to step over it and return an Object, keyed by the reference value.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 

// Define the 'toHash' function.
const toHash = (object, key) =>
  Array.prototype.reduce.call(
    object,
    (acc, data, index) => ((acc[!key ? index : data[key]] = data), acc),
    {}
  );

// Test the 'toHash' function with sample inputs.
toHash([4, 3, 2, 1]); 
toHash([{ a: 'label' }], 'a'); 

// A more in-depth example
let users = [{ id: 1, first: 'Jon' }, { id: 2, first: 'Joe' }, { id: 3, first: 'Moe' }];
let managers = [{ manager: 1, employees: [2, 3] }];
managers.forEach(
  manager =>
    (manager.employees = manager.employees.map(function(id) {
      return this[id];
    }, toHash(users, 'id')))
);

// Output the result.
console.log(managers); // Output: [ { manager: 1, employees: [ { id: 2, first: 'Joe' }, { id: 3, first: 'Moe' } ] } ]

Output:

[{"manager":1,"employees":[{"id":2,"first":"Joe"},{"id":3,"first":"Moe"}]}]

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-124-1 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that converts an array-like object into a hash map using a reducer function.
• Write a JavaScript function that iterates over an array-like structure and builds an object keyed by each element’s index.
• Write a JavaScript program that transforms an array into an object by mapping each element to a key-value pair via a callback.

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