Topic Description

Assuming you are developing a reading app that tracks users' reading sessions, the data is recorded in the following format:

const sessions = [
  { user: 8, duration: 50, books: ['The Hobbit'] },
  { user: 7, duration: 150, books: ['Pride and Prejudice'] },
  { user: 1, duration: 10, books: ['The Lord of the Rings'] },
  { user: 7, duration: 100, books: ['The Great Gatsby', 'Animal Farm'] },
  { user: 7, duration: 200, books: ['The Great Gatsby'] },
  { user: 2, duration: 200, books: ['1984'] },
  { user: 2, duration: 200, books: ['The Great Gatsby'] }

Each object has the following fields:

• user: The user's ID.
• duration: The reading duration in minutes.
• books: An array of book titles sorted alphabetically.

You need to implement a function called consolidateData to merge the reading data for each user according to the following rules:

• Merge data for the same user into a single object.
• Sum the duration fields.
• Merge the books arrays, remove duplicate titles, and sort them alphabetically.
• Preserve the original order of the results.
• If multiple entries belong to the same user, the consolidated entry should replace the earliest occurrence of that user in the original array.
• Do not modify the input objects.

Given the example input, the expected output is:

[
  { user: 8, duration: 50, books: ['The Hobbit'] },
  { user: 7, duration: 450, books: ['Animal Farm', 'Pride and Prejudice', 'The Great Gatsby'] },
  { user: 1, duration: 10, books: ['The Lord of the Rings'] },
  { user: 2, duration: 400, books: ['1984', 'The Great Gatsby'] },
]

Answer

function consolidateData(sessions){
	const userMap = new Set()
	const resultArray = []
	
	for (const session of sessions) {
		const { user, duration, books } = session
		
		if (userMap.has(user)) {
			const userDataIndex = resultArray.findIndex(userData => userData.user === user)
			resultArray[userDataIndex].duration += session.duration
			const booksList = Array.from(new Set( [...resultArray[userDataIndex].books, ...session.books] )) 
			resultArray[userDataIndex].books = booksList
		}else{
			userMap.add(user)
			resultArray.push({
				user,
				duration,
				books
			})
		}
	
	}
	return resultArray
}