This example shows how to add a custom function. First, you need to create a function:

...

 	public static decimal MySum(object value)
	{
		if (!ListExt.IsList(value))
		return Stimulsoft.Base.Helpers.StiValueHelper.TryToDecimal(value);

		return Stimulsoft.Data.Functions.Funcs.SkipNulls(ListExt.ToList(value))
		.TryCastToDecimal()
		.Sum();
	}

...

Next, use AddFunction() to add this function to StiFunctions:

...

	private void AddCustomFunction()
	{
		StiFunctions.AddFunction(
		"My Category", "MySum", "description",
		typeof(MyClass),
		typeof(decimal),
		"Calculates a sum of the specified set of values.",
		new[] { typeof(object) },
		new[] { "values" },
		new[] { "A set of values" }).UseFullPath = false;
	}
	
...

After that, you can use AddCustomFunction() in the main class after component initialization:

...

	public FormMain()
	{

		InitializeComponent();
		AddCustomFunction();
	}
	
...

На скриншоте ниже Вы можете увидеть результат выполнения данного кода: