Question

Using linq xml in c# how would I extract in for a given predecessor of SetSeg with a certain value in

Eg seatseg num =10 the following Seatassignment loc=??

<top> 
 <SeatSeg>
                  <Num>9</Num>
  </SeatSeg>
  <SeatAssignment>
                  <Loc>032A</Loc>
  </SeatAssignment>
  <SeatSeg>
                  <Num>10</Num>
  </SeatSeg>
  <SeatAssignment>
                  <Loc>033A</Loc>
  </SeatAssignment>
</top>

Answer 1

I ran this and it writes out 032A.

string xml = "<top><SeatSeg><Num>9</Num></SeatSeg><SeatAssignment><Loc>032A</Loc></SeatAssignment><SeatSeg><Num>10</Num></SeatSeg><SeatAssignment><Loc>033A</Loc></SeatAssignment></top>";
int seatNum = 10;
XDocument xDoc = XDocument.Parse(xml);

string seatLoc = (from seatSeg in xDoc.Element("top").Elements("SeatSeg")
                  where seatSeg.Element("Num").Value == seatNum.ToString() 
                  select seatSeg
                 ).Single().ElementsBeforeSelf().Last().Element("Loc").Value;

Console.WriteLine(seatLoc);

However, looking at the xml, it seems like the following which prints out 033A is what you want

string xml = "<top><SeatSeg><Num>9</Num></SeatSeg><SeatAssignment><Loc>032A</Loc></SeatAssignment><SeatSeg><Num>10</Num></SeatSeg><SeatAssignment><Loc>033A</Loc></SeatAssignment></top>";
int seatNum = 10;
XDocument xDoc = XDocument.Parse(xml);

string seatLoc = (from seatSeg in xDoc.Element("top").Elements("SeatSeg")
                  where seatSeg.Element("Num").Value == seatNum.ToString() 
                  select seatSeg
                 ).Single().ElementsAfterSelf().First().Element("Loc").Value;

Console.WriteLine(seatLoc);

ElementsBeforeSelf() will pull all the preceding siblings. Last() will get the last of the sequence.

Conversely, ElementsAfterSelf() will pull all the subsequent siblings. First() will get the first of the sequence.