字典组访问和IsChecked属性c#

我有一个字典的SelectNode类在SelectList类:

public Dictionary<long, SelectNode> Tbl;

SelectNode有以下属性:

        public long SectionId;
        public int State;
        public string Project;
        public string Name;
        public string VisitDate;
        public long Run;
        public SectionMsg Msg;
        public bool Checked;

在SelectList类中，我想创建由VisitDate分组的字典，其中只有Checked属性=true

这是我的方法:

    /// <summary>
    /// Method filters checkeditems from SelectNode class via SelectList class
    /// </summary>
    public void GetSelected()
    {
        foreach (SelectNode sn in this.Buf.Lst.Selected)
        {
           //Dont know what to put here to generate new dicationary
        }
    }

long SecdtionId是字典中的键。

var ordered = this.Buf.Lst.Selected.Where(o=> o.Value.Checked).GroupBy(o => DateTime.Parse(o.Value.VisitDate));

  var ordered = Tbl.Where(o=> o.Value.Checked).GroupBy(o => o.Value.VisitDate);