Merge pull request #1595 from yadavan88/sum-list-scala

Different ways to sum a list

Author: dominiqueplante

scala-core-modules/scala-core-numbers-2/src/main/scala/com/baeldung/scala/listsum/SumList.scala

@@ -0,0 +1,40 @@
+package com.baeldung.scala.listsum
+
+import scala.annotation.tailrec
+
+object SumList {
+
+  def sum(list: List[Int]): Int = list.sum
+
+  def sumByReduce(list: List[Int]): Int = list.reduceOption(_ + _).getOrElse(0)
+
+  def sumByFold(list: List[Int]): Int = list.foldLeft(0)(_ + _)
+
+  def sumByIteration(list: List[Int]): Int = {
+    var sum = 0
+    list.foreach(num => sum += num)
+    sum
+  }
+
+  def sumByFor(list: List[Int]): Int = {
+    var sum = 0
+    for (num <- list) { sum += num }
+    sum
+  }
+
+  def sumByTailRecursion(list: List[Int]): Int = {
+    @tailrec
+    def rec(list: List[Int], sum: Int): Int = {
+      list match {
+        case Nil       => sum
+        case a :: tail => rec(tail, sum + a)
+      }
+    }
+    rec(list, 0)
+  }
+
+  def sumNumeric[T](list: List[T])(using numeric: Numeric[T]): T = {
+    list.sum
+  }
+
+}

scala-core-modules/scala-core-numbers-2/src/test/scala/com/baeldung/scala/listsum/SumListUnitTest.scala

@@ -0,0 +1,57 @@
+package com.baeldung.scala.listsum
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.prop.TableDrivenPropertyChecks
+
+class SumListUnitTest
+  extends AnyFlatSpec
+  with Matchers
+  with TableDrivenPropertyChecks {
+
+  private val table = Table(
+    ("list", "expected sum"),
+    (List(1, 2, 3, 4), 10),
+    (List(0), 0),
+    (List.empty[Int], 0)
+  )
+
+  private val fns = List(
+    ("sum()", SumList.sum),
+    ("sumByFold()", SumList.sumByFold),
+    ("sumByReduce()", SumList.sumByReduce),
+    ("sumByIteration()", SumList.sumByIteration),
+    ("sumByFor()", SumList.sumByFor),
+    ("sumByTailRecursion()", SumList.sumByTailRecursion)
+  )
+
+  it should "calculate sum for a list" in {
+    forAll(table) { (input, expected) =>
+      fns map { (name, fn) =>
+        withClue(s"sum using the function `${name}` ") {
+          fn(input) shouldBe expected
+        }
+      }
+    }
+  }
+
+  it should "calculate sum for any numeric types" in {
+    val ints = List(1, 2, 3, 4)
+    SumList.sumNumeric(ints) shouldBe 10
+    SumList.sumNumeric(List.empty[Int]) shouldBe 0
+
+    val doubles = List(1d, 2d, 3d, 4d)
+    SumList.sumNumeric(doubles) shouldBe 10d
+
+    val bigints = List(BigInt(1), BigInt(2), BigInt(3), BigInt(4))
+    SumList.sumNumeric(bigints) shouldBe BigInt(10)
+
+  }
+
+  it should "calculate the sum of inside fields" in {
+    case class Item(price: Int)
+    val items = List(Item(1), Item(2), Item(3), Item(4))
+    items.foldLeft(0)((acc, item) => acc + item.price) shouldBe 10
+  }
+
+}