Hi

Question

datatable.select(filter expression, sort). here the filter expression which accepts the following condition?

Condition => datatable.select("UNIQUE NAME","NAME");

Here NAME Indicates the column in the table.....

Name

AAAA

BBBB

CCCC

AAAA

DDDD

CCCC

EEEE

Is it possible to get the unique name using filter condition?

Thanks & Regards

Manikandan Murugeshan

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Manikandan Murugeshan

Answer 1

What do you mean by Unique name? Not duplicates?

If so, take a look into this example I did:

        static void Main(string[] args)
        {
            DataTable table = new DataTable();
            table.Columns.Add("name", typeof(string));
            table.Rows.Add("aaa");
            table.Rows.Add("bbb");
            table.Rows.Add("ccc");
            table.Rows.Add("aaa");
            table.Rows.Add("bbb");

            DataTable newTable = RemoveDuplicateRows(table, "name");
        }

        public static DataTable RemoveDuplicateRows(DataTable dTable, string colName)
        {
            Hashtable hTable = new Hashtable();
            ArrayList duplicateList = new ArrayList();

            //Add list of all the unique item value to hashtable, which stores combination of key, value pair.
            //And add duplicate item value in arraylist.
            foreach (DataRow drow in dTable.Rows)
            {
                if (hTable.Contains(drow[colName]))
                    duplicateList.Add(drow);
                else
                    hTable.Add(drow[colName], string.Empty);
            }

            //Removing a list of duplicate items from datatable.
            foreach (DataRow dRow in duplicateList)
                dTable.Rows.Remove(dRow);

            //Datatable which contains unique records will be return as output.
            return dTable;
        }

---

Mitja

Answer 2

You could use the .ToTable(true) method of a DataView (or use the DataTable.DefaultView if you prefer). You can sort and filter a DataView. The DataView.ToTable(true) indicates that you wish distinct values. Try playing with it and see if it'll accomplish what you need ...

---

~~Bonnie Berent DeWitt [C# MVP]

geek-goddess-bonnie.blogspot.com

Answer 3

>>Is it possible to get the unique name using filter condition?

You can also do this：

public class MainTest
    {
        private class MyComparer : IEqualityComparer<DataRow>
        {
            public bool Equals(DataRow x, DataRow y)
            {
                if (x[0] == null && y[0] == null)
                {
                    return true;
                }
                else
                {
                    if (x[0] == null || y[0] == null)
                    {
                        return false;
                    }
                    else
                    {
                        return x[0].ToString() == y[0].ToString();
                    }
                }
            }

            public int GetHashCode(DataRow obj)
            {
                return obj[0].GetHashCode();
            }
        }
        static void Main(string[] args)
        {
            DataTable dt = new DataTable();
            dt.Columns.Add("name");
            dt.Rows.Add("AAA");
            dt.Rows.Add("BBB");
            dt.Rows.Add("AAA");
            dt.Rows.Add("CCC");
            dt.Rows.Add("AAA");
            dt.Rows.Add("CCC");

            var result = ((from row in dt.Rows.Cast<DataRow>()
                          select row).Distinct(new MyComparer())).ToArray();

            foreach (var item in result)
            {
                Console.WriteLine(item[0].ToString());
            }             
        }
    }

---

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Answer 4

Hi Mitja,

Am sorry . am not clearly defined my problem. My problem is i need to filter the Unique name in the "foreach" statement or using the keyword "UNIQUE" in "foreach" statement.

 DataTable table = new DataTable();
            table.Columns.Add("name", typeof(string));
            table.Columns.Add("age",typeof(string)); 
E.g => foreach(DataRow dt in datatable.select("Name='AAAA' and age > 24" )
{
}
In any DB we using query just as like this "SELECT * FROM datatable where NAME='AAAA' and age > 24". Same i used in "foreach" statement.
Same as we can use "SELECT DISTINCT NAME FROM datatable where age >24"
Like wise , is it possible to use "UNIQUE" keyword in "foreach" statement.
E.g : foreach(DataRow dt in datatable.select("UNIQUE NAME"))// it's not working, it's getting failed. any other alternate way?
{
}

---

Manikandan Murugeshan

Answer 5

Hi,

Am sorry . am not clearly defined my problem. My problem is i need to filter the Unique name in the "foreach" statement or using the keyword "UNIQUE" in "foreach" statement.

 DataTable table = new DataTable();
            table.Columns.Add("name", typeof(string));
            table.Columns.Add("age",typeof(string)); 
E.g => foreach(DataRow dt in datatable.select("Name='AAAA' and age > 24" )
{
}
In any DB we using query just as like this "SELECT * FROM datatable where NAME='AAAA' and age > 24". Same i used in "foreach" statement.
Same as we can use "SELECT DISTINCT NAME FROM datatable where age >24"
Like wise , is it possible to use "UNIQUE" keyword in "foreach" statement.
E.g : foreach(DataRow dt in datatable.select("UNIQUE NAME"))// it's not working, it's getting failed. any other alternate way?
{
}

---

Manikandan Murugeshan

Answer 6

Hi ,

Am sorry . am not clearly defined my problem. My problem is i need to filter the Unique name in the "foreach" statement or using the keyword "UNIQUE" in "foreach" statement.

 DataTable table = new DataTable();
            table.Columns.Add("name", typeof(string));
            table.Columns.Add("age",typeof(string)); 
E.g => foreach(DataRow dt in datatable.select("Name='AAAA' and age > 24" )
{
}
In any DB we using query just as like this "SELECT * FROM datatable where NAME='AAAA' and age > 24". Same i used in "foreach" statement.
Same as we can use "SELECT DISTINCT NAME FROM datatable where age >24"
Like wise , is it possible to use "UNIQUE" keyword in "foreach" statement.
E.g : foreach(DataRow dt in datatable.select("UNIQUE NAME"))// it's not working, it's getting failed. any other alternate way?
{
}

---

Manikandan Murugeshan

Answer 7

DataView.ToTable allows selecting distinct values.  See the example here: http://msdn.microsoft.com/en-us/library/wec2b2e6.aspx.  Hopefully this is what you are trying to achieve.

--
Mike

Answer 8

Hi Mike,

Am sorry . am not clearly defined my problem. My problem is i need to filter the Unique name in the "foreach" statement or using the keyword "UNIQUE" in "foreach" statement.

 DataTable table = new DataTable();
            table.Columns.Add("name", typeof(string));
            table.Columns.Add("age",typeof(string)); 
E.g => foreach(DataRow dt in datatable.select("Name='AAAA' and age > 24" )
{
}
In any DB we using query just as like this "SELECT * FROM datatable where NAME='AAAA' and age > 24". Same i used in "foreach" statement.
Same as we can use "SELECT DISTINCT NAME FROM datatable where age >24"
Like wise , is it possible to use "UNIQUE" keyword in "foreach" statement.
E.g : foreach(DataRow dt in datatable.select("UNIQUE NAME"))// it's not working, it's getting failed. any other alternate way?
{
}

---

Manikandan Murugeshan

Answer 9

I suggested an alternative way.  I hope you find what you are seeking.

--
Mike

Answer 10

Hi Mike,

First i apologize..... I didnt fully seen that Page.....  I looked for what i am seeking only.. then only i gone through the page fully, the example is very much similar to what i am looking for... really thanks a lot.....

---

Manikandan Murugeshan

Answer 11

That was my suggestion too (using DataView.ToTable(true)) ... but I didn't provide any links to look at, so I guess you didn't pay any attention. Oh well ... I like talking to myself. LOL!

---

~~Bonnie Berent DeWitt [C# MVP]

geek-goddess-bonnie.blogspot.com

Answer 12

Sorry, somehow I missed what you wrote too.  I will try reading your posts more often!

--
Mike

Answer 13

Hey,  no problem Mike! I was actually replying to Manikandan, not you ... and it was simply my attempt at being silly.  ;0)

---

~~Bonnie Berent DeWitt [C# MVP]

geek-goddess-bonnie.blogspot.com

Answer 14

Manikandan Murugeshan:-)

One problem can probably have many ways to solve itself……Have you tried mine？！

Haha……It's time for me you offer you a WHOLE solution：）

In fact you can use DataView to filter with some conditions，and then use ToTable to convert to the DataTable and then use my extended method:-)

public class MyComparer : IEqualityComparer<DataRow>
{
    public DataColumn Column { get; set; }

    public MyComparer(DataColumn _col)
    {
        Column = _col;
    }

    public bool Equals(DataRow x, DataRow y)
    {
        if (x[Column] == null && y[Column] == null)
        {
            return true;
        }
        else
        {
            if (x[Column] == null || y[Column] == null)
            {
                return false;
            }
            else
            {
                return x[Column].ToString() == y[Column].ToString();
            }
        }
    }

    public int GetHashCode(DataRow obj)
    {
        return obj[Column].GetHashCode();
    }
}

public static class DataTableUniqueExtender
{
    public static IEnumerable<string> GetUniqueFieldValues(this DataTable dt,Func<DataRow,bool>condition, string columnName)
    {
        //Tell whether the column exists in the DataTable
        if (dt.Columns.IndexOf(columnName) < 0)
        {
            throw new Exception("Column doesn't exist！");
        }

        var result = dt.AsEnumerable().Where(condition).Select(s => s).Distinct(new MyComparer(dt.Columns[columnName])).Select(s=>s[columnName].ToString());
        return result;
    }
}

public class MainTest
{
    static void Main(string[] args)
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("name");
        dt.Columns.Add("id");
        dt.Rows.Add("AAA", 1);
        dt.Rows.Add("AA", 2);
        dt.Rows.Add("AAA", 3);
        dt.Rows.Add("AAA", 1);
        dt.Rows.Add("AAA", 4);
        dt.Rows.Add("CCC", 2);

        var result = dt.GetUniqueFieldValues((row) => { return row["name"].ToString() == "AAA"; }, "id");

        foreach (var item in result)
        {
            Console.WriteLine(item[0].ToString());
        }
    }
}

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