[Solved] how to download gridview in excel in ASP.NET C #, ie How to use group by in datatable

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Ugh, be prepared for an accident that makes a mess of your data with this “associated by position” idea

I wouldn’t use LINQ for this either

var l = new List<string>();
string prev = null;
foreach(DataRow r in dt.Rows){
  var s = (string)r["Column1"];
  var t = (string)r["Column2"];

  if(s != prev){
    l.Add(s);
    prev = s;
  } 
  l.Add(t);
}

Desperate for something that uses LINQ?

var l = new List<string>();
var gg = dt.Rows.Cast<DataRow>().GroupBy(r => (string)r["Column1"]);
foreach(var g in gg){
  l.Add(g.Key);
  foreach(var r in g)
    l.Add((string)r["Column2"]);
}

So you want the output as a datatable – add to a datatable instead of a list:

var l = new DataTable();
l.Columns.Add("X");
string prev = null;
foreach(DataRow r in dt.Rows){
  var s = (string)r["Column1"];
  var t = (string)r["Column2"];

  if(s != prev){
    l.Rows.Add(s);
    prev = s;
  } 
  l.Rows.Add(t);
}

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solved how to download gridview in excel in ASP.NET C #, ie How to use group by in datatable