Question

I am trying to parse a rather long log file and creating a better more manageable listing of issues.

I am able to read and parse out the individual log line by line, but what I need to do is display only unique entries, as some errors occur more often than others and are always recorded with identical text.

What I was going to try to do was create a Dictionary object to hold each unique entry and as I work through the log file, search the Dictionary object to see if the same values are already in there.

Here is a crude sample of the code I have (a work in progress, I hope I have all syntax right) that does not work. For some reason this script never sees any distinct entries (if statement never passes):

    string[] rowdta = new string[4];
    Dictionary<string[], int> dict = new Dictionary<string[], int>();
    int ctr = -1;
    if (linectr == 1)
        {
            ctr++;
            dict.Add(rowdta, ctr);
        }
        else
        {
            foreach (KeyValuePair<string[], int> pair in dict)
            {
                if ((pair.Key[1] != rowdta[1]) || (pair.Key[2] != rowdta[2])| (pair.Key[3] != rowdta[3]))
                {
                    ctr++;
                    dict.Add(rowdta, ctr);
                }
            }
        }

Some sample data:
First line

    rowdta[0]="ErrorType";
    rowdta[1]="Undefined offset: 0";
    rowdta[2]="/url/routesDisplay2.svc.php";
    rowdta[3]="Line Number 5";

2nd line

    rowdta[0]="ErrorType";
    rowdta[1]="Undefined offset: 0";
    rowdta[2]="/url/routesDisplay2.svc.php";
    rowdta[3]="Line Number 5";

3rd line

    rowdta[0]="ErrorType";
    rowdta[1]="Undefined variable: fvmsg";
    rowdta[2]="/url/processes.svc.php";
    rowdta[3]="Line Number 787";

So, with this, the Dictionary will have 2 items in it, first line and 3rd line.

I have also tried this with the following which nalso does not find any variations in the log file text.

    if (!dict.ContainsKey(rowdta)) {}

Can someone please help me get this syntax right? I am just a newbie at C# but this should be relatively straightforward. As always, I am thinking that this should be enough information to get the conversation started. If you want/need more detail, please let me know.

Answer 1

Either create a wrapper for your strings which implements IEquatable.

public class LogFileEntry :IEquatable<LogFileEntry>
{
    private readonly string[] _rows;

    public LogFileEntry(string[] rows)
    {
        _rows = rows;
    }

    public override int GetHashCode()
    {
        return 
            _rows[0].GetHashCode() << 3 | 
            _rows[2].GetHashCode() << 2 | 
            _rows[1].GetHashCode() << 1 | 
            _rows[0].GetHashCode();
    }

    #region Implementation of IEquatable<LogFileEntry>

    public override bool Equals(Object obj)
    {
        if (obj == null) 
            return base.Equals(obj);

        return Equals(obj as LogFileEntry);  
    } 

    public bool Equals(LogFileEntry other)
    {
        if(other == null) 
            return false;

        return _rows.SequenceEqual(other._rows);
    }

    #endregion
}

Then use that in your dictionary:

var d = new Dictionary<LogFileEntry, int>();

var entry = new LogFileEntry(rows);
if( d.ContainsKey(entry) )
{
    d[entry] ++;
} 
else
{
    d[entry] = 1;
}

Or create a custom comparer similar to that proposed by @dasblinkenlight and use as follows

public class LogFileEntry 
{
}

public class LogFileEntryComparer : IEqualityComparer<LogFileEntry>{ ... }

var d = new Dictionary<LogFileEntry, int>(new LogFileEntryComparer());

var entry = new LogFileEntry(rows);
if( d.ContainsKey(entry) )
{
    d[entry] ++;
} 
else
{
    d[entry] = 1;
}