RowFilter from a textbox value

Farhan Shariff

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();

12 Replies

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Vulpes12y ago
Accepted answer
I think I must have had a mental aberration when making my opening post in this thread since whilst we can't use external variables directly in the Select method and RowFilter properties we can certainly use their current values:

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;
string expr = "Delta_sigma < " + delta_sigma_critical;
rows4 = table1.Select(expr);

foreach (DataRow r in rows4)
{
r.Delete();
r.AcceptChanges();
}

double Non_critical_cpk = double.Parse(textBox2.Text);//ideal value = 6

double critical_cpk = double.Parse(textBox3.Text);//ideal value = 1.6

// --part1

DataView dv = table1.DefaultView;
dv.RowFilter = "NOT(CpK_Refrence > " + Non_critical_cpk + " AND CpK > " + Non_critical_cpk + ")";
table1 = dv.ToTable();

// --part2

DataView dv1 = table1.DefaultView;
dv1.RowFilter = "CpK < " + critical_cpk + " AND Delta_Sigma > " + delta_sigma_critical;
DataTable dt2 = dv1.ToTable();
dv1.RowFilter = "NOT(CpK < " + critical_cpk + " AND Delta_Sigma > " + delta_sigma_critical + ")";
DataTable dt3 = dv1.ToTable();
dt2.Merge(dt3);
table1 = dt2;
dv1 = null;
dt2 = dt3 = null;
Farhan Shariff12y ago
Perfect :)
Vulpes12y ago
Sorry, I should have called AcceptChanges on the DataTable as a whole to get rid of the deleted records:

foreach (DataRow r in rows4)
{
r.Delete();
}

table1.AcceptChanges();
Farhan Shariff12y ago
there is error

foreach (DataRow r in rows4)
{
r.Delete();
r.AcceptChanges();// Error : Cannot perform this operation on a row not in the table.
}
Vulpes12y ago
Yes, you've summed it up nicely :)

It's a point worth remembering as it can lead to difficult to find bugs if you don't spot it early.
Farhan Shariff12y ago
I understand what you are saying Since the index is reduced elements are not examined(scanned).
Vulpes12y ago
If you iterate forwards through a collection using a for loop and delete an element from it, then the indices of the remaining elements will all be reduced by 1. This means that the next element will not be examined unless you reduce the control variable by 1 as well.

If you're deleting multiple elements, it's therefore easier to iterate backwards through the collection because each time you delete an element it won't affect the indices of the elements which are still to be examined.
Farhan Shariff12y ago
I TRUST you :) ...let me compile the code I want to know what is the use of using inverse for loop. for(int i = table1.Rows.Count - 1; i >= 0; i--) when I used the normal for loop the values where not filtered
Farhan Shariff12y ago
//part1-----------------------got the first part

double Non_critical_cpk = double.Parse(textBox2.Text);//ideal value =6
Convert.ToDouble(Non_critical_cpk);
for (int v = table1.Rows.Count - 1; v >= 0; v--)
{
double c = Convert.ToDouble(table1.Rows[v]["CpK_Refrence"].ToString());
double c1 = Convert.ToDouble(table1.Rows[v]["CpK"].ToString());
if (c > (Non_critical_cpk) && c1 > (Non_critical_cpk))
{
table1.Rows.RemoveAt(v);
}

}

//-----------part2 -------
Farhan Shariff12y ago
how to modify this ?

columns (Delta_sigma,CpK,CpK_Refrence)
text box(delta_sigma_critical,Non_critical_cpk,critical_cpk).

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

double Non_critical_cpk = double.Parse(textBox2.Text);//ideal value =6

double critical_cpk = double.Parse(textBox3.Text);//Ideal value = 1.6

//-----------------------------------------------------------------------------------
// --part1

DataView dv = table1.DefaultView;
dv.RowFilter = "NOT(CpK_Refrence > Non_critical_cpk AND CpK >Non_critical_cpk)";
table1 = dv.ToTable();

//-------------------------------------------------------------------------------------
//----------------------part2
DataView dv1 = table1.DefaultView;
dv1.RowFilter = "CpK < critical_cpk AND Delta_Sigma > delta_sigma_critical";
DataTable dt2 = dv1.ToTable();
dv1.RowFilter = "NOT(CpK < critical_cpk AND Delta_Sigma > delta_sigma_critical)";
DataTable dt3 = dv1.ToTable();
dt2.Merge(dt3);
table1 = dt2;
dv1 = null;
dt2 = dt3 = null;
Farhan Shariff12y ago
Ok . what about RowFilter can it use 'external' variables
Vulpes12y ago
The problem here is that you're trying to use an 'external' variable in the Select method which isn't allowed.

Try this code instead:

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

for(int i = table1.Rows.Count - 1; i >= 0; i--) //EDITED
{
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);
}