i need fast and convenient way to organize table data in-memory

Question

Initial conditions:

DateTime moment

string key

double value

somewhere across the code i want to

Add("2010.08.09 12:55:34", "px_ValX", 10);
Add("2010.08.09 12:55:35", "px_ValX", 1);
Add("2010.08.09 12:55:35", "px_ValY", 12);
Add("2010.08.09 12:55:35", "px_ValZ", 100);
Add("2010.08.09 12:55:38", "px_ValZ", 5); 

and then i want to get table from that data array

DataTable ToTable()

which produces

date|px_valX|px_ValY|px_ValZ
"2010.08.09 12:55:34"|10|0|0
"2010.08.09 12:55:35"|1|12|100
"2010.08.09 12:55:38"|0|0|5

Also it would be awesome if i could do fast

double Get(DateTime moment, string key)

and

DataTable Get(string key) 

which produces the following table

data|value
"2010.08.09 12:55:34"|10

It's rather SQL task, but i need in-memory data structure. I plan to use C# DataTable class and its Select method, but i think there is more fast and convenient way.

Right on this moment i use the following class in my app

[Serializable]
public class CalcItem
{
    public CalcItem()
    {
        Additional = new Dictionary<string, double>();
    }
    public Dictionary<string, double> Additional { get; set; }

    public DateTime Date { get; set; }
}

and in CalcItemManager

public List<CalcItem> CalcItems { get; set; }

To add data i do

var clc = new CalcItem();
clc.Additional.Add("px_ValX", 10);
_dataManager.CalcItems.Add(clc);

Answer 1

Here is my another question that overheads this one and is a solution