Count all columns start with special name in C#

Question

I have a DataTable have all columns like:

B0_1 A1_1 B0_2 A1_2 B0_3 A1_3 B0_4 A1_4

How to count only columns start with A1_?

I had variably contains A1_x like this:

nameCol + n.ToString() + "_" +

Note: In this example you can see A1_1 -> A1_4 but 4 is randoms number, about from 1 -> 9.

`columns.Count( col => col.Name.StartsWith("A1_") && col.Name.Length == 4 )` ? — CompuChip, Jul 27 '16 at 09:38
I want to count only columns start with `A1_x` with 1 < x < 9. — Ave, Jul 27 '16 at 09:38
@User2012384 Sometimes people say "count" when they mean "sum". Or you could count unique values in the columns. Or unique values in _all_ columns. — CompuChip, Jul 27 '16 at 09:39
So given your example the outcome of the count would be 4, right? — rene, Jul 27 '16 at 09:41
Do you want to know the amount of columns? Or count something regarding those cells' contents? — Andrew, Jul 27 '16 at 09:43
Thanks, all people. #user3185569 and #compuchip were helpful me. — Ave, Jul 27 '16 at 09:52

score 4 · Accepted Answer · answered Jul 27 '16 at 09:38

4

I suggest using Linq:

  DataTable table = ...

  int result = table.Columns
    .OfType<DataColumn>()
    .Count(column => column.ColumnName.StartsWith("A1_"));

answered Jul 27 '16 at 09:38

Dmitry Bychenko

180,369
20
160
215

Thanks a lot... You awesome! – Ave Jul 27 '16 at 09:50
It would be better to use `.Cast()` instead of `.OfType()` because you don't need filter the elements. Read [here](http://stackoverflow.com/questions/4015930/when-to-use-cast-and-oftype-in-linq) the difference between these two methods. – Alberto Spelta Jul 27 '16 at 10:01

Zein Makki · Answer 2 · 2016-07-27T09:48:37.697

Regex is one option to match the post-fix restriction (A1_x with 1 < x < 9):

DataTable dt = new DataTable();
dt.Columns.Add("A1_a"); // out
dt.Columns.Add("A1_6"); // in
dt.Columns.Add("A1_5"); // in
dt.Columns.Add("A1_7"); // in
dt.Columns.Add("A1_0"); // out
dt.Columns.Add("A1_1"); // out
dt.Columns.Add("A1_9"); // out

// count result is: 3

var count = (from col in dt.Columns.OfType<DataColumn>()
             where Regex.IsMatch(col.ColumnName, "A1_[2-8]")
             select col).Count();

You need to add using System.Text.RegularExpressions; to use the Regex type.

score 0 · Answer 3 · edited Jul 27 '16 at 09:51

0

Using LINQ

int count = table.Columns.Cast<DataColumn>()
                  .Count(c => c.ColumnName.StartsWith("A1_"));

Using foreach

int count = 0;
foreach(DataColumn dc in table)
{
    if (dc.ColumnName.StartsWith("A1_"))
        count++;
}

edited Jul 27 '16 at 09:51

Alberto Spelta

3,578
2
21
20

answered Jul 27 '16 at 09:44

Imad

7,126
12
55
112

Count all columns start with special name in C#

3 Answers3