如何过滤与模式匹配的字符串列表

Question

I have a list of strings (file names actually) and I'd like to keep only those that match a filter expression like: \*_Test.txt .

What would be the best to achieve this?

Here is the answer that I came up with:

List<string> files = new List<string>();
files.Add("MyFile1.csv");
files.Add("MyFile1_Test.txt");
files.Add("MyFile2.csv");
files.Add("MyFile2_Test.txt");
files.Add("MyFile3.csv");
files.Add("MyFile3_Test.txt");
files.Add("MyFile_Testtxttxt.txt");

// Define a filter
string filter = "*_Test.txt";

// Make the filter regex safe
foreach (char x in @"\+?|{[()^$.#")
    filter = filter.Replace(x.ToString(), @"\" + x.ToString());

filter = string.Format("^{0}$",filter.Replace("*", ".*"));

// Old School
List<string> resultList1 = files.FindAll(delegate(string s) { return Regex.IsMatch(s, filter, RegexOptions.IgnoreCase); });

// Version using LINQ
List<string> resultList2 = files.Where(x =>  Regex.IsMatch(x, filter, RegexOptions.IgnoreCase) == true ).ToList();

Answer 1

You probably want to use a regular expression for this if your patterns are going to be complex....

you could either use a proper regular expression as your filter (eg for your specific example it would be new Regex(@"^.*_Test\.txt$") or you could apply a conversion algorithm.

Either way you could then just use linq to apply the regex.

for example

var myRegex=new Regex(@"^.*_Test\.txt$");
List<string> resultList=files.Where(myRegex.IsMatch).ToList();

Some people may think the above answer is incorrect, but you can use a method group instead of a lambda. If you wish the full lamda you would use:

var myRegex=new Regex(@"^.*_Test\.txt$");
List<string> resultList=files.Where(f => myRegex.IsMatch(f)).ToList();

or non Linq

List<string> resultList=files.FindAll(delegate(string s) { return myRegex.IsMatch(s);});

if you were converting the filter a simple conversion would be

 var myFilter="*_Test.txt";
 var myRegex=new Regex("^" + myFilter.Replace("*",".*") +"$");

You could then also have filters like "*Test*.txt" with this method.

However, if you went down this conversion route you would need to make sure you escaped out all the special regular expression chars eg "." becomes @".", "(" becomes @"(" etc.......

Edit -- The example replace is TOO simple because it doesn't convert the. so it would find "fish_Textxtxt" so escape atleast the .

so

string myFilter="*_Test.txt";
foreach(char x in @"\+?|{[()^$.#") {
  myFilter = myFilter.Replace(x.ToString(),@"\"+x.ToString());
}
Regex myRegex=new Regex(string.Format("^{0}$",myFilter.Replace("*",".*")));

Answer 2

Have you tried LINQ:

List<string> resultList = files.Where(x => x.EndsWith("_Test.txt")).ToList();

or if you are running this on some old/legacy .NET version (< 3.5):

List<string> resultList = files.FindAll(delegate(string s) { 
    return s.EndsWith("_Test.txt"); 
});

Answer 3

This worked for me and is fairly simple:

List<string> keys = new List<string>();
//populate your list
var myregex = new Regex("^.+$");
List<string> matchlist = keys.Where(i=>myregex.IsMatch(i)).ToList();