JavaScript: Invert the key-value pairs of an object, without mutating it

JavaScript fundamental (ES6 Syntax): Exercise-78 with Solution

Write a JavaScript program to invert the key-value pairs of an object, without mutating it. The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.

• Use Object.keys() and Array.prototype.reduce() to invert the key-value pairs of an object and apply the function provided (if any).
• Omit the second argument, fn, to get the inverted keys without applying a function to them.
• The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const invertKeyValues = (obj, fn) =>
  Object.keys(obj).reduce((acc, key) => {
    const val = fn ? fn(obj[key]) : obj[key];
    acc[val] = acc[val] || [];
    acc[val].push(key);
    return acc;
  }, {});
console.log(invertKeyValues({ a: 1, b: 2, c: 1 }));
console.log(invertKeyValues({ a: 1, b: 2, c: 1 }, value => 'group' + value));

Sample Output:

{"1":["a","c"],"2":["b"]}
{"group1":["a","c"],"group2":["b"]}

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-78-1 by w3resource (@w3resource) on CodePen.

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