Performing a subtotal on filtered data from a streamreader

Question

edit as question is unanswered

I have a filtered output based on 1 criteria (first 3 numbers are 110,210 or 310,to give 3 distinct groups) to console from streamreader.

Answer 1

(Posting this answer here, as the other question is closed.) Using ReadAllText will be inefficient for large files.

public static class LinqToTextReader {
    public static IEnumerable AsEnumerable(this TextReader reader) {
        string line;
        while ((line = reader.ReadLine()) != null) {
            yield return line;
        }
    }
}

class Program {
    static void Main(string[] args) {
        using (StreamReader reader = new StreamReader("file.dat")) {
            var locations = new Dictionary() {
                {"210", new [] {406, 409, 129, 140, 142, 153}},
                {"310", new [] {322, 325, 113, 124, 126, 137}},
                {"410", new [] {478, 481, 113, 124, 126, 137}}
            };

            var query =
                from line in reader.AsEnumerable()
                let lineStart = line.Substring(0, 3)
                where lineStart == "210" || lineStart == "310" || lineStart == "410"
                let currentLocations = locations[lineStart]
                select new {
                    letters = line.Substring(currentLocations[0], currentLocations[1]),
                    value =
                        int.Parse(line.Substring(currentLocations[2], currentLocations[3])) +
                        int.Parse(line.Substring(currentLocations[4], currentLocations[5]))
                };

            //It should be possible to combine the two queries
            var query2 = 
                from item in query
                group item by item.letters into letterGroup
                select new {
                    letters = letterGroup.Key,
                    total = letterGroup.Sum(item => item.value)
                };

            foreach (var item in query2) {
                Console.WriteLine(item.letters);
                Console.WriteLine(item.total);
            }
        }
    }
}