how to convert the entire content of a DataTable column to a delimited string in C#?

Question

I am retrieving data from an MSSQL server using the SqlDataAdapter and DataSet. From that DataSet I am creating a DataTable. My goal is to convert each column of the table into a string where the elements are comma delimited. I figured that I would try the string conversion first before making the delimiter work.

The code runs in the code-behind of an ASP.Net page. The ultimate goal is to pass the string to a jscript variable, it's a "functional requirement" that I create a delimited string from the columns and that it has to end up as a jscript variable.

Here's what I have thus far:

    DataSet myDataSet = new DataSet();
    mySqlDataAdapter.Fill(myDataSet);
    DataTable temperature = myDataSet.Tables["Table"];

    // LOOP1
    foreach (DataRow row in temperature.Rows)
    // this loop works fine and outputs all elements
    // of the table to the web page, this is just to
    // test things out
    {
        foreach (DataColumn col in temperature.Columns)
        {
            Response.Write(row[col] + " ### ");
        }
        Response.Write("<br>");
    }

    // LOOP2
    foreach (DataColumn column in temperature.Columns)
    // this loop was meant to take all elements for each
    // column and create a string, then output that string
    {
        Response.Write(column.ToString() + "<br>");
    }

In LOOP1 things work fine. My data has 4 columns, all are appropriately rendered with one record per row on the web page.

I saw the code for LOOP2 at http://msdn.microsoft.com/en-us/library/system.data.datacolumn.tostring.aspx which seems to do exactly what I need except it does not actually do what I want.

The only thing LOOP2 does is write 4 lines to the web page. Each line has the header of the respective table column but none of the additional data. Clearly there's either a logic flaw on my part or I misunderstand how DataColumn and .toString for it works. Please help me out on this one. Thanks in advance.

EDIT: Here's an SQL query result example, this is what the Table looks like: Table quesry result @ ImageShack

What I want to end up are four strings, here's an example for the string that would be created from the second column: "-6.7, -7, -7.2, -7.3, -7.3".

Answer 1

This code will concatenate values from cells under each column with ", " :

foreach (var column in temperature.Columns)
{
    DataColumn dc = column as DataColumn;
    string s = string.Join(", ", temperature.Rows.OfType<DataRow>()
                                                 .Select(r => r[dc]));
    // do whatever you need with s now
}

For example, for DataTable defined as:

DataTable table = new DataTable();
table.Columns.Add(new DataColumn("Column #1"));
table.Columns.Add(new DataColumn("Column #2"));
table.Rows.Add(1, 2);
table.Rows.Add(11, 22);
table.Rows.Add(111, 222);

... it will produce "1, 11, 111" and "2, 22, 222" strings.

---

Edit: I saw you chose to declare column as var as opposed to DataColumn, is that a matter of personal preference/style or is there an issue with coding?

Consider following scenario (on the same data table example as above):

// we decide we'll use results later, storing them temporarily here
List<IEnumerable<string>> columnsValues = new List<IEnumerable<string>>();
foreach (DataColumn column in temperature.Columns)
{
    var values = temperature.Rows.OfType<DataRow>()
                                 .Select(r => r[column].ToString())
    columnsValues.Add(values);
}

We assume we now got list of list of column values. So, when we print them, like this:

foreach (var lisOfValues in columnsValues)
{
    foreach (var value in listOfValues)
    {
        Debug.Write(value + " ");
    }

    Debug.WriteLine("");
}

We expect to see 1 11 111 followed by 2 22 222 . Right?

Wrong .

This code will output 2 22 222 twice. Why? Our .Select(r => r[column].ToString()) captures column variable - not its value, but variable itself - and since we don't use it immediately, once we're out of loop all we know is last value of column .

To learn more about this concept search for closures and captured variables - for example, in posts like this .

Summary :

In this very case you can go with DataColumn in foreach statement. It doesn't matter here because we're enumerating through our .Select(r => r[dc]) either way inside the loop (precisely, string.Join does that for us), producing results before we get to next iteration - whatever we capture, is used immediately.

Answer 2

The link you have posted clearly states

The Expression value, if the property is set; otherwise, the ColumnName property.

and that is what is happening. You get column names.

Answer 3

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