Experiment with statistic - 1

kmath-core/src/commonMain/kotlin/scientifik/kmath/stat/Stat.kt

@@ -0,0 +1,71 @@
+package scientifik.kmath.stat
+
+import scientifik.kmath.operations.Field
+import scientifik.kmath.operations.RealField
+import scientifik.kmath.operations.Ring
+import scientifik.kmath.operations.Space
+import scientifik.kmath.structures.NDStructure
+import kotlin.math.pow
+
+
+
+
+// TODO tailrec
+fun <T> Ring<T>.pow(element : T, n : Int) : T {
+    if (n == 0 ){
+        return one
+    }
+    if (n==1){
+        return element
+    }
+    val temp = pow(element, n / 2)
+    return if (n%2==0) temp*temp else element*temp*temp
+}
+
+//fun <T,R> NDStructure<T>.map(transform : (T) -> R) : NDStructure<R>{
+//
+//}
+
+
+/**
+ * Context for sequence-like operations
+ */
+class CollectionsOperations<T>(val context: Space<T>){
+    fun sum(structure: NDStructure<T>): T {
+        return with(context){
+            var sum = zero
+            for (element in structure.elements()) {
+                sum += element.second
+            }
+            sum
+        }
+    }
+
+}
+
+/**
+ * Context for statistical operations
+ */
+open class Statistical<T>(val context : Field<T>){
+        fun mean(data : NDStructure<T>) = moment(data, 1)
+
+        fun variance(data: NDStructure<T>) = centralMomentum(data, 2)
+
+        fun moment(data: NDStructure<T>, k : Int) : T{
+            return with(context){
+                var result = zero
+                val number = data.shape.reduce { acc, i -> acc*i }
+                for (element in data.elements()){
+                    result += pow(element.second, k)
+                }
+                result/number
+            }
+        }
+
+        fun centralMomentum(data: NDStructure<T>, k: Int) = with(context){moment(data, k) - pow(mean(data), k)}
+
+}
+
+class RealStatistical : Statistical<Double>(RealField){
+    fun std(data : NDStructure<Double>) = with(context){variance(data).pow(0.5)}
+}