C# compare 2 files contents for matches

Question

I am trying to find a way to compare some text in 2 files and if a match is found then run a process.

Here are examples of the files;

'File A' = Automated list of text with this format;

example1
ex2
289 Example
fht_nkka

'File B' = File names from a directory search;

example1
test2
test4785

Using my 2 example files, I want to search them both and find matches.

So 'File A' above contains 'example1' and 'example1' is in 'File B'. What I want to be able to do is create 'string[] match based on all matches. Is there an easy way of doing this?

NOTE: these files do not always have the same line data or amount of lines in.

Answer 1

1. Use System.IO.File.ReadAllLines() on each of the two files to create two string arrays.
2. Create a sorted version of array containing filenames to improve search performance. You can use LINQ for this purpose.
3. Given that your first file has a fixed layout, your required filename should always be at Line No. 4 for each record, so you can use a for loop on your second array with fixed increment to read the required filename.
4. Use Array.BinarySearch() to quickly locate whether that required filename exists in the list of files (the other array that is).

Here is a rough sketch of the code:

string[] AllRecs = System.IO.File.ReadAllLines(FIRST_FILE_PATH);
string[] AllFileNames = System.IO.File.ReadAllLines(SECOND_FILE_PATH);
Array.Sort(AllFileNames);

for (int i = 3; i < AllRecs.Length; i += 8) 
{
    if (Array.BinarySearch(AllFileNames, AllRecs(i) + ".exe") >= 0)
        System.Diagnostics.Process.Start(AllRecs(i) + ".exe");

}

Answer 2

Managed to sort this out, here is what I have done;

var fileAcontents = File.ReadAllLines(fileA);
var fileBcontents = File.ReadAllLines(fileB);

HashSet<string> hashSet = new HashSet<string>(fileAcontents);
foreach (string i in fileBList)
{
    if (hashSet.Contains(i))
    {
        // <- DO SOMETHING :)
    }
}

Answer 3

//Keep in a list of strings with FileA contents 

List<string> linesOfFileA = new List<string>();
string line ;

using (StreamReader sr = new StreamReader(pathToFileA)) 
{
    //read each line of fileA
    line = sr.ReadLine();
    while(line != null)
    {
        linesOfFileA.Add(line) ;
        line = sr.ReadLine();
    }
}
//Now read the contents of FileB

string fileWithoutExtension ;
int posOfExtension ;

using (StreamReader srB = new StreamReader(pathToFileB)) 
{
    //read each line of fileB
    line = sr.ReadLine();
    while(line != null)
    {
        posOfExtension = line.LastIndexOf(".");

        if(posOfExtension < 0)
        {
            fileWithoutExtension = line ;
        }               
        else
        {
            fileWithoutExtension = line.Substring(0,posOfExtension) ;
        }

        //Check to see if the FileA contains file but without Extension
        if(linesOfFileA.Contains(fileWithoutExtension))
        {
            //Store into another list / or execute here
        }
        line = sr.ReadLine();
    }
}

In the first part of the code you skip the number of lines that you need, but because of the current shown format they will not affect your comparison

Answer 4

Fill a dictionary object with File A contents then loop through File B contents querying File A dictionary object. Reason for dictionary object is its speed if you have a large array of data.

Dictionary<int, string> FileA = new Dictionary<int, string>();
string sFileAList = dataFileA;

Loop through File A contents and add to Dict where i is a counter.

int count = 0;
foreach (string s in sFileAList.split('\n')) {
    count++;
    if (count > 3) FileA.Add(i, s);
}

Then compare while looping through File B contents.

foreach (string s in dataFileB.split('\n')) {
    if (FileA.ContainsValue(s)) {
        // Run exe
    }
}