build.gradle

@@ -1,5 +1,5 @@
 buildscript {
-    ext.kotlin_version = '1.2.60'
+    ext.kotlin_version = '1.2.61'
 
     repositories {
         mavenCentral()

kmath-common/src/main/kotlin/scientifik/kmath/misc/Cumulative.kt

@@ -0,0 +1,59 @@
+package scientifik.kmath.misc
+
+import kotlin.jvm.JvmName
+
+
+/**
+ * Generic cumulative operation on iterator
+ * @param T type of initial iterable
+ * @param R type of resulting iterable
+ * @param initial lazy evaluated
+ */
+fun <T, R> Iterator<T>.cumulative(initial: R, operation: (T, R) -> R): Iterator<R> = object : Iterator<R> {
+    var state: R = initial
+    override fun hasNext(): Boolean = this@cumulative.hasNext()
+
+    override fun next(): R {
+        state = operation.invoke(this@cumulative.next(), state)
+        return state
+    }
+}
+
+fun <T, R> Iterable<T>.cumulative(initial: R, operation: (T, R) -> R): Iterable<R> = object : Iterable<R> {
+    override fun iterator(): Iterator<R> = this@cumulative.iterator().cumulative(initial, operation)
+}
+
+fun <T, R> Sequence<T>.cumulative(initial: R, operation: (T, R) -> R): Sequence<R> = object : Sequence<R> {
+    override fun iterator(): Iterator<R> = this@cumulative.iterator().cumulative(initial, operation)
+}
+
+fun <T, R> List<T>.cumulative(initial: R, operation: (T, R) -> R): List<R> = this.iterator().cumulative(initial, operation).asSequence().toList()
+
+//Cumulative sum
+
+@JvmName("cumulativeSumOfDouble")
+fun Iterable<Double>.cumulativeSum() = this.cumulative(0.0){ element, sum -> sum + element}
+
+@JvmName("cumulativeSumOfInt")
+fun Iterable<Int>.cumulativeSum() = this.cumulative(0){ element, sum -> sum + element}
+
+@JvmName("cumulativeSumOfLong")
+fun Iterable<Long>.cumulativeSum() = this.cumulative(0L){ element, sum -> sum + element}
+
+@JvmName("cumulativeSumOfDouble")
+fun Sequence<Double>.cumulativeSum() = this.cumulative(0.0){ element, sum -> sum + element}
+
+@JvmName("cumulativeSumOfInt")
+fun Sequence<Int>.cumulativeSum() = this.cumulative(0){ element, sum -> sum + element}
+
+@JvmName("cumulativeSumOfLong")
+fun Sequence<Long>.cumulativeSum() = this.cumulative(0L){ element, sum -> sum + element}
+
+@JvmName("cumulativeSumOfDouble")
+fun List<Double>.cumulativeSum() = this.cumulative(0.0){ element, sum -> sum + element}
+
+@JvmName("cumulativeSumOfInt")
+fun List<Int>.cumulativeSum() = this.cumulative(0){ element, sum -> sum + element}
+
+@JvmName("cumulativeSumOfLong")
+fun List<Long>.cumulativeSum() = this.cumulative(0L){ element, sum -> sum + element}

kmath-common/src/test/kotlin/scientifik.kmath.misc/CumulativeKtTest.kt

@@ -0,0 +1,13 @@
+package scientifik.kmath.misc
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class CumulativeKtTest {
+    @Test
+    fun testCumulativeSum() {
+        val initial = listOf(-1.0, 2.0, 1.0, 1.0)
+        val cumulative = initial.cumulativeSum()
+        assertEquals(listOf(-1.0, 1.0, 2.0, 3.0), cumulative)
+    }
+}