Manipulating Column in DataTable C#

Question

Am using DataTable in C# and am trying to manipulate, modify one of the column. Consider sample data below

Id     City Temperature
-------------------
1       A   -12

2       B    23

3       C    12

And after conversion i want the below result where am converting Minus to M and Positive values to P

Id     City Temperature
-------------------------
1       A    12M

2       B    23P

3       C    12P

Can i achieve this using LINQ..Am parsing this with around 50k Rows and dont want to compromise on performance.what are the other best ways ?

so you want to create a new datatable with a new column where the data-type is string? — Tim Schmelter
– Tim Schmelter, Commented Nov 11, 2014 at 12:10
@TimSchmelter Exactly but prefer same DataTable by converting the datatype !! is it possible to change the DataType also fine!! — Peru
– Peru, Commented Nov 11, 2014 at 12:16
No, it's not possible to change the type of a column of a filled DataTable. I've provided an answer which shows how to create a new table. — Tim Schmelter
– Tim Schmelter, Commented Nov 11, 2014 at 12:20

Tim Schmelter · Accepted Answer · 2014-11-11 13:11:43Z

2

If the column is string instead of double/int:

foreach(DataRow row in table.Rows)
{
    string temp = row.Field<string>("Temperature");
    bool negative = temp.StartsWith("-");
    temp = negative ? temp.Substring(1) + "M" : temp + "P";
    row.SetField("Temperature", temp);
}

If the column type is double - as mentioned now - you have to create a new DataTable. You cannot change the DataType after the Datatable is filled with data.

DataTable newTable = table.Clone();
int ordinal = newTable.Columns.IndexOf("Temperature");;
newTable.Columns.Remove("Temperature");  // remove double-column
DataColumn tempCol = newTable.Columns.Add("Temperature"); // string
tempCol.SetOrdinal(ordinal); 
foreach (DataRow row in table.Rows)
{
    DataRow newRow = newTable.Rows.Add();
    foreach(DataColumn col in newTable.Columns)
    {
        if (col == tempCol)
        {
            double temp = row.Field<double>("Temperature");
            bool negative = temp < 0;
            double abs = Math.Abs(temp);
            string newTemp = negative ? abs.ToString() + "M" : abs.ToString() + "P";
            newRow.SetField(col, newTemp);
        }
        else
            newRow.SetField(col, row[col.ColumnName]);
    }
}

edited Nov 11, 2014 at 13:11

answered Nov 11, 2014 at 12:10

Tim Schmelter

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1 Comment

Peru Over a year ago

Thanks @TimSchmelter Will take a look !!! +1 will mark answer after i resolve this !! Thanks again!!

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