using System;
using System.Globalization;
using System.Linq;
using System.Collections.Generic;
 
public class Test
{
 
 
	public static void Main()
	{
            string text = "Count([AssignedTo]) as [AssignedTo] , Sum([Billing Amount]) as [Billing Amount] , Max([Billing Rate]) as [Billing Rate] , Min([ExecutionDate]) as [ExecutionDate] , Average([HoursSpent]) as [HoursSpent] , [Project], [Sub-Project], [TaskName], [Vendor], [Work Classification], [Work Done], Count([WorkItemType]) as [WorkItemType] ";
            var aggregates = new []{ "Count", "Sum", "Max", "Min", "Average"};
            var all = text.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries)
                .Select(col => new{ col, token = col.TrimStart().Split().First() })
                .Where(x => x.token.Contains('(') && aggregates.Any(a => x.token.StartsWith(a)))
                .Select(x => x.token);
            foreach(string aggregateCol in all)
                Console.WriteLine(aggregateCol);
	}
}

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