将文本框值与DataTable列进行比较 [英] compare textbox value with DataTable column

问题描述

我试图通过将它与文本框中输入的值进行比较来删除列（Delta_sigma）中的一些数据，但是我得到错误无法对System.Double和System.String执行'<'操作。

I am trying to delete some data in column (Delta_sigma) by comparing it with value entered in textbox but i get error Cannot perform '<' operation on System.Double and System.String.

 DataColumn Delta_sigma = table1.Columns.Add("Delta_Sigma", typeof(double));

Delta_sigma.Expression = "(Convert(Median,'System.Double') -                                        Convert(Median_Refrence,'System.Double')) / (sigma_Refrence)";
 
double delta_sigma_critical = double.Parse(textBox1.Text);


DataRow[] rows4;
 rows4 = table1.Select("  Delta_sigma < delta_sigma_critical ");
            foreach (DataRow r in rows4)
                r.Delete();

推荐答案

Quote：

无法对System.Double和System.String执行'<'操作。

Cannot perform '<' operation on System.Double and System.String.

非常清楚。你无法比较不同类型的数据。



因此，尝试比较相同类型的数据。

Quite clear. You cannot compare data of different types.

So, try to compare data with same type.

double delta_sigma_critical = double.Parse(textBox1.Text);

for(int i = table1.Rows.Count - 1; i >= 0; i--)
{
   double d = Convert.ToDouble(table1.Rows[i]["Median"].ToString()) - Convert.ToDouble(table1.Rows[i]["Median_Refrence"].ToString());
   d /= Convert.ToDouble(table1.Rows[i]["sigma_Refrence"].ToString());
   if (d < delta_sigma_critical) table1.Rows.RemoveAt(i);
}

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