Reading the next line using LINQ and File.ReadAllLines()

Question

Hi,

I have a file which represents items, in one line there's Item GUID followed by 5 lines describing the item.

Example:

Line 1: Guid=8e2803d1-444a-4893-a23d-d3b4ba51baee name= line1 
Line 2: Item details = bla bla   
.  
.  
Line 7: Guid=79e5e39d-0c17-42aa-a7c4-c5fa9bfe7309 name= line7 
Line 8: Item details = bla bla    
.  
. 

I am trying to access this file first to get the GUIDs of the items meet the criteria provided using LINQ e.g. where line.Contains("line1").. This way I will get the whole line, I will extract the GUID from there, I want to pass this GUID to another function which should access the file "again", find that line (where line.Contains("line1") && line.Contains("8e2803d1-444a-4893-a23d-d3b4ba51baee") and reads the next 5 lines starting from that line.

Is there any efficient way to do so?

Answer 1

I don't think it really makes sense to use LINQ entirely given the requirements of what you need to do and given that the index of the line in the array is fairy integral. I would also recommend doing everything in one pass - opening the file multiple times won't be as efficient as just reading everything once and processing it immediately. As long as the file is structured as well as you describe, this won't be terribly difficult:

    private void GetStuff()
    {
        var lines = File.ReadAllLines("foo.txt");
        var result = new Dictionary<Guid, String[]>();
        for (var index = 0; index < lines.Length; index += 6)
        {
            var item = new
            {
                Guid = new Guid(lines[index]),
                Description = lines.Skip(index + 1).Take(5).ToArray()
            };
            result.Add(item.Guid, item.Description);
        }
    }

Answer 2

I tried a couple different ways to do this with LINQ but nothing allowed me to do a single scan of the file. For this scenario you're talking about I would go down to the Enumerable level and use the GetEnumerator like this:

public IEnumerable<LogData> GetLogData(string filename)
{
    var line1Regex = @"Line\s(\d+):\sGuid=([0123456789abcdefg]{8}-[0123456789abcdefg]{4}-[0123456789abcdefg]{4}-[0123456789abcdefg]{4}-[0123456789abcdefg]{12})\sname=\s(\w*)";
    int detailLines = 4;

    var lines = File.ReadAllLines(filename).GetEnumerator();
    while (lines.MoveNext())
    {
        var line = (string)lines.Current;
        var match = Regex.Match(line, line1Regex);
        if (!match.Success)
             continue;

        var details = new string[detailLines];
        for (int i = 0; i < detailLines && lines.MoveNext(); i++)
        {
            details[i] = (string)lines.Current;
        }

        yield return new LogData
        {
            Id = new Guid(match.Groups[2].Value),
            Name = match.Groups[3].Value,
            LineNumber = int.Parse(match.Groups[1].Value),
            Details = details
        };
    }
}