Concatenating LINQ query results when using loops

Question

I need to do a loop over a bunch of files and spit out log entries through a LINQ query:

foreach (string file in Directory.EnumerateFiles(TextBoxLogDirectory.Text, "*.log"))
{
    FileStream stream = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.ReadWrite | FileShare.Delete);
    using (LogReader reader = new LogReader(stream))
    {
        var events = (from x in reader.Parse().Where(y => y.IsInRange(range) && (y.EventNo == 1180 || y.EventNo == 1187) && y.GetDefaultMessageField().Contains(":Outbound/"))
                      group x by x.GetDefaultMessageField() into grouping
                      select new
                      {
                          ID = grouping.Key,
                          Event1180 = grouping.LastOrDefault(z => z.EventNo == 1180),
                          Event1187 = grouping.LastOrDefault(z => z.EventNo == 1187)
                      }).ToList();
    }
}

This query must run on a single file at a time, and the above works fine, but I need to keep appending the results of the query to an object outside of the foreach loop. Something like this (although this doesn't work, unfortunately):

dynamic events; // I want to append to this object outside of the loop's scope.
foreach (string file in Directory.EnumerateFiles(TextBoxLogDirectory.Text, "*.log"))
{
    FileStream stream = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.ReadWrite | FileShare.Delete);
    using (LogReader reader = new LogReader(stream))
    {
        events = (from x in reader.Parse().Where(y => y.IsInRange(range) && (y.EventNo == 1180 || y.EventNo == 1187) && y.GetDefaultMessageField().Contains(":Outbound/"))
                      group x by x.GetDefaultMessageField() into grouping
                      select new
                      {
                          ID = grouping.Key,
                          Event1180 = grouping.LastOrDefault(z => z.EventNo == 1180),
                          Event1187 = grouping.LastOrDefault(z => z.EventNo == 1187)
                      }).ToList().Concat(events);
    }
}

How can I achieve this sort of behavior?

Not sure if it helps, my query above will return objects with (string)ID, (LogEvent)Event1180, and (LogEvent)Event1187.

Vlad · Accepted Answer · 2014-08-20 20:45:43Z

2

You can try something like this:

Directory.EnumerateFiles(TextBoxLogDirectory.Text, "*.log")
         .SelectMany(ParseFile);

where ParseFile is defined as

IEnumerable<string> ParseFile(string file)
{
    using (FileStream stream =
               new FileStream(file, FileMode.Open, FileAccess.Read,
                              FileShare.ReadWrite | FileShare.Delete))
    using (LogReader reader = new LogReader(stream))
    {
        return (from x in reader.Parse()
                   .Where(y => y.IsInRange(range) &&
                          (y.EventNo == 1180 || y.EventNo == 1187) &&
                          y.GetDefaultMessageField().Contains(":Outbound/"))
                group x by x.GetDefaultMessageField() into grouping
                select new
                {
                    ID = grouping.Key,
                    Event1180 = grouping.LastOrDefault(z => z.EventNo == 1180),
                    Event1187 = grouping.LastOrDefault(z => z.EventNo == 1187)
                }).ToList();
    }
}

Or you can inline the helper function, if you want to.

This produces an IEnumerable<string>, which you perhaps should immediately materialize with ToList.

Edit: Oh, I see, we've got a type mismatch.

There are two ways of working around this: either you should name the anonymous type and make the function return IEnumerable<that type>, or just inline the function content into a lambda:

Directory.EnumerateFiles(TextBoxLogDirectory.Text, "*.log")
         .SelectMany(file =>
    {
        using (FileStream stream =
                   new FileStream(file, FileMode.Open, FileAccess.Read,
                                  FileShare.ReadWrite | FileShare.Delete))
        using (LogReader reader = new LogReader(stream))
        {
            return (from x in reader.Parse()
            // ...
                }).ToList();
        }
    }
);

edited Aug 20, 2014 at 20:45

answered Aug 20, 2014 at 20:32

Vlad

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5 Comments

Alexandru Over a year ago

This doesn't work. It complains about the "select" statement which is part of the "select new" with the following error: "Error 2 Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<AnonymousType#1>' to 'System.Collections.Generic.IEnumerable<string>'. An explicit conversion exists (are you missing a cast?)"

Vlad Over a year ago

@Alexandru: One more important correction: added ToList into the parser function, as it's closing the reader!

Alexandru Over a year ago

Yes, I see now...all I needed to do was actually create a class with three public methods...one string, one LogEvent, and another LogEvent, whose names must match that of my query, and I can "select new <ClassTypeName>"

Vlad Over a year ago

@Alexandru: yes, but you can avoid it if you inline the function as at the bottom of the answer.

Alexandru Over a year ago

Interesting. See, there's a lot of things about LINQ I never knew and learn every day. Thanks!

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