How to add a new element into a DenseVector

Question

I need to add a new element (double value) into an existing DenseVector. I found some workarounds, however, what is the right way how to do this in Math.NET?

Answer 1

There is currently no "intended" way to do it. The Matrix type does have InsertRow/InsertColumn methods, and there has been some demand to add an Insert method also for the Vector type. I've just opened a new ticket #159 to track it.

In the meantime, you could use the following routine (I'm using v3.0.0-alpha5 here):

Vector<T> InsertAt<T>(Vector<T> v, int i, T value) where T : struct, IEquatable<T>, IFormattable
{
    var res = Vector<T>.Build.Dense(v.Count+1);
    if (i > 0) v.Storage.CopySubVectorTo(res.Storage, 0, 0, i, true);
    if (i < v.Count) v.Storage.CopySubVectorTo(res.Storage, i, i+1, v.Count-i, true);
    res.At(i, value);
    return res;
}

var v = Vector<double>.Build.Dense(5, i => i);
var vx = InsertAt(v, 5, 100);