Run aggregate on datatable column

I had one table with columns "Name" and "Department" which i need to display in a multiline textbox. like below
Name~~~~~~~~ Dept
Tarun Ghosh~~~SWD
Diptangshu Das~SSWD
So that the names and Dept are aligned properly. So i needed the Max of the string length of the column "Name" and give a right-padding to name to make all of same length with the maximum lengthed name.
Firstly i went with the primitive looping through each record and calculate the max of the row, if it is greater than the global max, set global max to current max algo...
But i was not satisfied with the approach even though no problem.
Then i got the

public Object Compute(
 string expression,
 string filter
)

function of DataTable. Expression par needs to be some aggregate function lik Sum, Avg,Min,Max,Count,Var. with filter expression is same as where clause in dt.Select() function.
But one problemmmmmmmm.... The expression parameter can't work on computed column. Like say you have two column qty and unit price. You need to get the max(qty*unitPrice), then first you have to add a new column to hold the value of the multiplied result and then use the compute function on that column.
So in my case i wanted to get the max of length. So i added a column as

           DataColumn col = new DataColumn("Length");
           col.Expression = "Len(Name)";
           col.DataType = typeof(int);
           dt.Columns.Add(col);
           object obj= dt.Compute("Max(Length)","");
           Response.Write(obj.ToString());

obj is storing the max length value
Some useful link
Link1
Link2

Send Balk Data(Datatable) From Child Window To Parent

Currently in one of my .aspx page i was selecting some information from a child window which is opened from a parent window. I opened the window like
window.open('PartNoLookup.aspx','PartNo','left=150, top=60,width=800,height=600, toolbar=no, status=1,scrollbars=yes,resizable=no,dependent=yes');
Some PartNos with their information was selected by the child "PartNoLookup.aspx" page. Now i have to send the part nos to the parent page to be displayed. My parent page was NewQuote.aspx.
Now the problem arises if it was a small value then i could do it with
window.opener.document.getelementById('parentCtrlId').value='Some Value'
But as it was a bulk datatable i can't send it like that.
I stored the DataTable in Session["PartNo"] from the child page. And placed a hidden field "hidFlag" (not with runat='server'. this should be a html hiddenfield) in the Parent Page (i.e. NewQuote.aspx). And wrote some javascript with the Page.ClientScript.RegisterStartupScript like
Page.ClientScript.RegisterStartupScript(typeof(string), "", "refreshParentAndClose();", true);
And inside childpage (PartNoLookup.aspx) i added the JS function refreshParentAndClose() as
function refreshParentAndClose()
{
window.opener.document.getelementById('parentCtrlId').value='checksession'
window.opener.document.forms[0].submit();
window.close();
}
So this function will set the flag in the parent a also submit the page.
Here as the page is postback by some unconventional way, only the PageLoad,PreRender and some processing cycle events will fire in the parent. So i have to check for the flag inside tha Load() event. So i added the checking code in Page_LoadCode as
if(Request.Form["hidFlag"]!=null)
{
string flag=Request.Form["hidFlag"];
switch(flag)
{
case "checksession":
//Check the session and show inside the page.
break;
}
}

Note:Put the hidden field as Html hidden, not with runat=server coz, if you set it server variable then change by the javascript will no be visible as it will be restored from the viewstate. y JavaScript we are changing the value not the stored value inside Encripted ViewState. Also if you use server Hidden field the clientid may not be same as server id. So setting it from child page will be problemetic (but not impossible).