Near the Norbulingka Institute, Dharamshala, India
Near the Norbulingka Institute, Dharamshala, India

Scala collections provide you three options for sorting: sorted(), sortWith() and sortBy(). Here is a simplified explanation:

sorted

Will sort the list using the natural ordering (based on the implicit Ordering passed)

sortBy (an attribute)

Sort by a given attribute using the attribute’s type. e.g. given a list of Person objects, if you want to sort them in ascending order of their age (which is an Int), you could simply say:

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	personList.sortBy(_.age)

sortWith (a function)

Takes a comparator function. Useful when you want to specify a custom sorting logic. e.g. if you want to sort by age descending, you could write this as:

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	personList.sortWith{(leftE,rightE) =>
	     leftE.age > rightE.age
	}

Or, more simply:

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	personList.sortWith(_.age > _.age)

A full example

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	// Sequence of numbers
	val xs = Seq(1, 5, 3, 4, 6, 2)

	// Sort using Natural ordering as defined for Integers in Scala Library
	xs.sorted //1,2,3,4,5,6

	// Sort 'with' a comparator function
	xs.sortWith(_<_) //1,2,3,4,5,6
	xs.sortWith(_>_) //6,5,4,3,2,1
	xs.sortWith((left,right) => left > right) //6,5,4,3,2,1

	// Create a Person class
	case class Person(val name:String, val age:Int)

	// Define a list of Persons
	val ps = Seq(Person("John", 32), Person("Bruce", 24), Person("Cindy", 33), Person("Sandra", 18))

	// Sort People by increasing Age (natural ordering of Int will kick in)
	ps.sortBy(_.age) //List(Person(Sandra,18), Person(Bruce,24), Person(John,32), Person(Cindy,33))


	// Sort People by decreasing Age, using a comparator function
	ps.sortWith(_.age > _.age) //List(Person(Cindy,33), Person(John,32), Person(Bruce,24), Person(Sandra,18))