Converting datatable column to double C# - csv

Question

I read some columns from a csv file and then display it in a DataGridView. The column "Value" contains some 3-digit integer values. I want to have this integer values shown in the datagridview as doubles with one decimals place. The conversion doesn't seem to work. Also when I load a large csv file (around 30k rows) it is loaded immediately but with conversion it takes too much time.
using (StreamReader str = new StreamReader(openFileDialog1.FileName)) {
CsvReader csvReadFile = new CsvReader(str);
dt = new DataTable();
dt.Columns.Add("Value", typeof(double));
dt.Columns.Add("Time Stamp", typeof(DateTime));
while (csvReadFile.Read()) {
var row = dt.NewRow();
foreach (DataColumn column in dt.Columns) {
row[column.ColumnName] = csvReadFile.GetField(column.DataType, column.ColumnName);
}
dt.Rows.Add(row);
foreach (DataRow row1 in dt.Rows)
{
row1["Value"] = (Convert.ToDouble(row1["Value"])/10);
}
}
}
dataGridView1.DataSource = dt;

Answer 1

Sounds like you have two questions:
How to format the value to a single decimal place of scale.
Why does the convert section of code take so long?
Here are possibilities
See this answer which specifies a possibility of using
String.Format("{0:0.##}", (Decimal) myTable.Rows[rowIndex].Columns[columnIndex]);
You are iterating over every row of the datatable every time you read a line. That means when you read line 10 of the CSV, you will iterate over rows 1-9 of the DataTable again! And so on for each line you read! Refactor to pull that loop out of the ReadLine... something like this:
using (StreamReader str = new StreamReader(openFileDialog1.FileName)) {
CsvReader csvReadFile = new CsvReader(str);
dt = new DataTable();
dt.Columns.Add("Value", typeof(double));
dt.Columns.Add("Time Stamp", typeof(DateTime));
while (csvReadFile.Read()) {
var row = dt.NewRow();
foreach (DataColumn column in dt.Columns) {
row[column.ColumnName] = csvReadFile.GetField(column.DataType, column.ColumnName);
}
dt.Rows.Add(row);
}
foreach (DataRow row1 in dt.Rows)
{
row1["Value"] = (Convert.ToDouble(row1["Value"])/10);
}
}
dataGridView1.DataSource = dt;