c# - LINQ First() or Single() parameter -

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trying sorted data csv file. code works fine except "side" column string , same 1 group. can't figure out parameter should single() of first() methods. 

    var stuff = line in file.readlines(@"d:\tmp\4.csv").skip(1)                     let columns = line.split(';')                     select new                     {                         time = columns[0],                         side = columns[2],                         qty = columns[3],                         symbol = columns[4],                         price = columns[5],                     };          var sorted = line in stuff                      group line new { line.time, line.symbol }                          category                          select new {                              category.key.time,                              category.key.symbol,                               qty = category.sum(p => int32.parse(p.qty)),                              price = category.average(p => double.parse(p.price)),                              side = ?????? };

single throw exception if finds more 1 record, think not want

first select first record list, both single , first throw 'invalidoperationexception' exception if collection empty.

so use firstordefault here 

side = category.select(p => p.side).firstordefault()

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