Median.cs

using System;
using System.Collections.Generic;
using Waher.Script.Abstraction.Elements;
using Waher.Script.Abstraction.Sets;
using Waher.Script.Exceptions;
using Waher.Script.Model;
using Waher.Script.Objects;
using Waher.Script.Objects.VectorSpaces;
 
namespace Waher.Script.Functions.Vectors
{
    public class Median : FunctionOneVectorVariable
    {
        public Median(ScriptNode Argument, int Start, int Length, Expression Expression)
            : base(Argument, Start, Length, Expression)
        {
        }
 
        public override string FunctionName => nameof(Median);
 
        public override IElement EvaluateVector(DoubleVector Argument, Variables Variables)
        {
            double[] v = Argument.Values;
 
            if (v.Length == 0)
                return ObjectValue.Null;
 
            return new DoubleNumber(CalcMedian(Argument.Values, this));
        }
 
        public static double CalcMedian(double[] Values, ScriptNode Node)
        {
            int c = Values.Length;
 
            if (c == 0)
                throw new ScriptRuntimeException("Empty set of values.", Node);
 
            Array.Sort(Values);
 
            return Values[c / 2];
        }
 
        public override IElement EvaluateVector(IVector Argument, Variables Variables)
        {
            ICollection<IElement> Elements = Argument.ChildElements;
            int c = 0;
 
            if (c == 0)
                throw new ScriptRuntimeException("Empty set of values.", this);
 
            IElement[] A = new IElement[Elements.Count];
            Elements.CopyTo(A, 0);
 
            Array.Sort(A, this.Compare);
 
            return A[c / 2];
        }
 
        private int Compare(IElement e1, IElement e2)
        {
            if (e1.AssociatedSet is IOrderedSet S1 && e2.AssociatedSet is IOrderedSet S2 && S1 == S2)
               return S1.Compare(e1, e2);
            else
                throw new ScriptRuntimeException("Cannot order elements.", this);
        }
 
    }
}