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

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

Invert Key-Value Pairs in Object

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
// Define the function 'invertKeyValues' to invert the keys and values of an object, optionally applying a function to the values.
const invertKeyValues = (obj, fn) =>
  // Use Object.keys() to get an array of keys of the object, then reduce it to create a new object with inverted keys and values.
  Object.keys(obj).reduce((acc, key) => {
    // Apply the optional function to the value or use the value directly.
    const val = fn ? fn(obj[key]) : obj[key];
    // If the inverted value does not exist in the accumulator object, initialize it as an empty array.
    acc[val] = acc[val] || [];
    // Push the original key into the array associated with the inverted value.
    acc[val].push(key);
    return acc; // Return the updated accumulator object.
  }, {});

// Example usage:
console.log(invertKeyValues({ a: 1, b: 2, c: 1 })); // Outputs: { '1': ['a', 'c'], '2': ['b'] }
console.log(invertKeyValues({ a: 1, b: 2, c: 1 }, value => 'group' + value)); // Outputs: { group1: ['a', 'c'], group2: ['b'] }

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.

For more Practice: Solve these Related Problems:

• Write a JavaScript program that inverts an object’s keys and values, grouping keys that share the same value into an array.
• Write a JavaScript function that creates a new object by swapping each key-value pair of the input object.
• Write a JavaScript program that handles duplicate values by mapping them to arrays of original keys in the inverted object.

Improve this sample solution and post your code through Disqus

Previous: Write a JavaScript program to iterate over all own properties of an object, running a callback for each one.
Next: Write a JavaScript program to take any number of iterable objects or objects with a length property and returns the longest one.