JavaScript: Group the elements into two arrays, depending on the provided function's truthiness for each element

JavaScript fundamental (ES6 Syntax): Exercise-168 with Solution

Group Elements by Predicate Truthiness

Write a JavaScript program to group the elements into two arrays, depending on the provided function's truthiness for each element.

• Use Array.prototype.reduce() to create an array of two arrays.
• Use Array.prototype.push() to add elements for which fn returns true to the first array and elements for which fn returns false to the second one.

Sample Solution:

JavaScript Code:

// Define a function 'partition' that partitions an array based on the result of a provided function 'fn'
const partition = (arr, fn) =>
  // Use the reduce method to iterate over the array and partition its elements
  arr.reduce(
    // Callback function with accumulator 'acc', current value 'val', index 'i', and the original array 'arr'
    (acc, val, i, arr) => {
      // Push the current value 'val' into the appropriate partition array based on the result of 'fn(val, i, arr)'
      acc[fn(val, i, arr) ? 0 : 1].push(val);
      // Return the updated accumulator 'acc' for the next iteration
      return acc;
    },
    // Initialize the accumulator as an array containing two empty arrays
    [[], []]
  );
// Define an array 'users' containing objects representing users with 'user', 'age', and 'active' properties
const users = [{ user: 'barney', age: 36, active: false }, { user: 'fred', age: 40, active: true }];
// Partition the 'users' array based on the 'active' property of each user object
partition(users, o => o.active);
// Log the original 'users' array
console.log(users);

Output:

[{"user":"barney","age":36,"active":false},{"user":"fred","age":40,"active":true}]

Flowchart:

Live Demo:

For more Practice: Solve these Related Problems:

• Write a JavaScript program that splits an array into two arrays based on whether each element passes a predicate function.
• Write a JavaScript function that groups items into "truthy" and "falsy" arrays using a provided test function.
• Write a JavaScript program that returns an object with keys "true" and "false", each containing elements based on predicate evaluation.
• Write a JavaScript function that partitions an array into two groups by evaluating each element’s truthiness with a custom predicate.

Improve this sample solution and post your code through Disqus

Previous: Write a JavaScript program to calculate how many numbers in the given array are less or equal to the given value using the percentile formula.
Next: Write a JavaScript program to create a function that invokes fn with partials appended to the arguments it receives.