c# - LINQ query string[] group by multiple anonymous columns -

i have delimited file reading string array (file has no headers) , trying parse linq query.

i want group multiple anonymous columns (using array indexes) , sum 1 of fields.

for instance, have file in format:

1000200034,2015,abc,1

1000200034,2015,def,2

i want group first , second columns, disregard third, , sum fourth.

so return:

1000200034,2015,3

when group single column, can result return sum:

ienumerable<string[]> query = row in data                     row[0] == "1000200034"                     group row row[0] g                     select new string[]                     {                         g.key,                         g.sum(a=>int.parse(a.elementat(3))).tostring(),                        }; 

but if try add other column, no longer sum, both rows returned:

 ienumerable<string[]> query = row in data                     row[0] == "1000200034"                     group row new[]{row[0], row[1]} g                     select new string[]                     {                         g.key[0],                         g.key[1],                         g.sum(a=>int.parse(a.elementat(3))).tostring(),                        }; 

i'm pretty new linq , c#, sql background solid. having hard time converting know. appreciated!

the problem due grouping new [] should new, have specify field names anonymous types used in group, like:

ienumerable<string[]> query = row in data                               row[0] == "1000200034"                               group row new { firstkey = row[0], secondkey = row[1] } g                               select new string[]         {             g.key.firstkey,             g.key.secondkey,             g.sum(a=>int.parse(a.elementat(3))).tostring(),            }; 

with method syntax should like:

ienumerable<string[]> query2 = data.where(row => row[0] == "1000200034")     .groupby(row => new { firstkey = row[0], secondkey = row[1] })     .select(grp => new string[]     {         grp.key.firstkey,         grp.key.secondkey,         grp.sum(a => int.parse(a.elementat(3))).tostring(),     });