如何计算C＃中数据项在数据表的列中出现的次数

Question

I have created a datatable with two columns, "Function" and "Date". This table records the date that each of n functions is used on a website. I want to extract the number of times that a particular function such as "Access" appears in the table. Any help will be appreciated.

DataTable table = new DataTable();

table.Columns.Add("Function", typeof(string));
table.Columns.Add("Date", typeof(datetime));

table.Rows.Add(Access, 01/08/2012);
table.Rows.Add(Load, 01/08/2012);
table.Rows.Add(Save, 01/08/2012);
table.Rows.Add(Access, 02/08/2012);
table.Rows.Add(Print, 02/08/2012);

int accessCount = 0;

foreach (DataRow row in table.Rows)
{
    if (row["Function"] == "Access")
    {
        accessCount++;
    }
}

Answer 1

var results = table.AsEnumerable()
    .GroupBy(row => row.Field<string>("Function"))
    .Select(group => new 
    {
        Function = group.Key,
        Count = group.Count(),
    });

Answer 2

You can use linq for it

var result = from rec in table.AsEnumerable 
             group rec by rec.Field<string>("Function") into g 
             select new { Function = g.Key, Count = g.Count()}

Answer 3

You can use Linq-To-Datatable and Enumerable.GroupBy to group by your function. Then you can use ToDictionary to build a dictionary with the function as key and the count as value:

var functionLookup = table.AsEnumerable()
    .GroupBy(r => r.Field<string>("Function"))
    .ToDictionary(g => g.Key, g => g.Count());

int accessCount = functionLookup["Access"];  // 2

Note that it's case sensitive by default. If you want it to be case insensitive you would need to pass the appropriate IEqualityComparer for the key, in this case:

.ToDictionary(g => g.Key, g => g.Count(), StringComparer.OrdinalIgnoreCase);