Collections Operations

Code

val nums = (1 to 10).toList

// map / filter
val doubled = nums.map(_ * 2)
val evens = nums.filter(_ % 2 == 0)

// fold / reduce
val sum = nums.foldLeft(0)(_ + _)
val product = nums.reduce(_ * _)

// groupBy
val grouped = nums.groupBy(_ % 3)
// Map(0 -> List(3,6,9), 1 -> List(1,4,7,10), 2 -> List(2,5,8))

// flatMap / flatten
val nested = List(List(1,2), List(3,4))
nested.flatten       // List(1,2,3,4)
nested.flatMap(_.map(_ * 10))  // List(10,20,30,40)

Explanation

Scala collections provide a rich set of higher-order functions. foldLeft takes a seed and accumulates; reduce is a special case without a seed; groupBy partitions by a key function. These are lazy on views and strict on concrete collections.

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