Few questions about LINQ to Object

[Sudip_inn]

1) Why author used here SelectMany() instead of select ?

XDocument xmlDocTargetFile = XDocument.Load(ADM_File_Path);

//removing duplicate data
xmlDocTargetFile.Descendants("TickerBrokerDateFormatMap").GroupBy(row =>
new
{
StandardDate = row.Element("StandardDate").Value,
Broker_Id = row.Attribute("Broker_Id").Value,
BrokerTab_Id = row.Attribute("BrokerTab_Id").Value
})
//.Where(grp => grp.Count() > 1)
.SelectMany(m => m.Skip(1)).Remove();

xmlDocTargetFile.Save(ADM_File_Path);

Why author used here SelectMany() instead of Select() ?
please discuss with example to understand.

2)

can we use .Select() before where() ?

string strActualProvidedByCompany = dtColoInfo.AsEnumerable()
.Where(j => j.Field<string>("Section").ToUpper() == strSection.ToUpper()
&& j.Field<string>("LineItem").ToUpper() == strLineItem.ToUpper()
&& j.Field<string>("Period").ToUpper() == strPeriod.ToUpper())
.Select(a => a.Field<string>("ActualProvidedByCompany")).FirstOrDefault();

probably i tried to write Select() before where then i was getting error but the moment i place Select() after Where() then error gone. in sql we write select first and then filter. in LINQ can't we use select before WHERE() ?

tell me why i was getting error when i place select() before where() ?

please discuss my 2 question with example to better understand. thanks

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