How to count of sub-string occurrences?

C# Problem Overview

Suppose I have a string like:

MyString = "OU=Level3,OU=Level2,OU=Level1,DC=domain,DC=com";

then I want to know how many time of occurrences of sub-string "OU=" in this string. With single char, maybe there is something like:

int count = MyString.Split("OU=").Length - 1;

but Split only works for char, not string.

Also how to find the position of n occurrences? For example, the position of 2nd "OU=" in the string?

How to resolve this issue?

C# Solutions

Solution 1 - C#

Regex.Matches(input, "OU=").Count

Solution 2 - C#

You can find all the occurrences and their positions with IndexOf:

string MyString = "OU=Level3,OU=Level2,OU=Level1,DC=domain,DC=com";
string stringToFind = "OU=";

List<int> positions = new List<int>();
int pos = 0;
while ((pos < MyString.Length) && (pos = MyString.IndexOf(stringToFind, pos)) != -1)
{
    positions.Add(pos);
    pos += stringToFind.Length();
}

Console.WriteLine("{0} occurrences", positions.Count);
foreach (var p in positions)
{
    Console.WriteLine(p);
}

You can get the same result from a regular expression:

var matches = Regex.Matches(MyString, "OU=");
Console.WriteLine("{0} occurrences", matches.Count);
foreach (var m in matches)
{
    Console.WriteLine(m.Index);
}

The primary differences:

The Regex code is shorter
The Regex code allocates a collection and multiple strings.
The IndexOf code could be written to output the position immediately, without creating a collection.
It's likely that the Regex code will be faster in isolation, but if used many times the combined overhead of the string allocations could cause a much higher load on the garbage collector.

If I were writing this in-line, as something that didn't get used often, I'd probably go with the regex solution. If I were to put it into a library as something to be used a lot, I'd probably go with the IndexOf solution.

Solution 3 - C#

(Clippy-mode:ON)

You look like you're parsing an LDAP query!

Would you like to parse it:

manually? Goto "SplittingAndParsing"
Automagically via Win32 calls? Goto "Using Win32 via PInvoke"

(Clippy-mode:OFF)

"SplittingAndParsing":

var MyString = "OU=Level3,OU=Level2,OU=Level1,DC=domain,DC=com";
var chunksAsKvps = MyString
    .Split(',')
    .Select(chunk => 
        { 
            var bits = chunk.Split('='); 
            return new KeyValuePair<string,string>(bits[0], bits[1]);
        });

var allOUs = chunksAsKvps
    .Where(kvp => kvp.Key.Equals("OU", StringComparison.OrdinalIgnoreCase));

"Using Win32 via PInvoke":

Usage:

var parsedDn = Win32LDAP.ParseDN(str);    
var allOUs2 = parsedDn
    .Where(dn => dn.Key.Equals("OU", StringComparison.OrdinalIgnoreCase));

Utility Code:

// I don't remember where I got this from, honestly...I *think* it came
// from another SO user long ago, but those details I've lost to history...
public class Win32LDAP
{
   #region Constants
   public const int ERROR_SUCCESS = 0;
   public const int ERROR_BUFFER_OVERFLOW = 111;
   #endregion Constants

   #region DN Parsing
   [DllImport("ntdsapi.dll", CharSet = CharSet.Unicode)]
   protected static extern int DsGetRdnW(
       ref IntPtr ppDN, 
       ref int pcDN, 
       out IntPtr ppKey, 
       out int pcKey, 
       out IntPtr ppVal, 
       out int pcVal
   );

   public static KeyValuePair<string, string> GetName(string distinguishedName)
   {
       IntPtr pDistinguishedName = Marshal.StringToHGlobalUni(distinguishedName);
       try
       {
           IntPtr pDN = pDistinguishedName, pKey, pVal;
           int cDN = distinguishedName.Length, cKey, cVal;

           int lastError = DsGetRdnW(ref pDN, ref cDN, out pKey, out cKey, out pVal, out cVal);

           if(lastError == ERROR_SUCCESS)
           {
               string key, value;

               if(cKey < 1)
               {
                   key = string.Empty;
               }
               else
               {
                   key = Marshal.PtrToStringUni(pKey, cKey);
               }

               if(cVal < 1)
               {
                   value = string.Empty;
               }
               else
               {
                   value = Marshal.PtrToStringUni(pVal, cVal);
               }

               return new KeyValuePair<string, string>(key, value);
           }
           else
           {
               throw new Win32Exception(lastError);
           }
       }
       finally
       {
           Marshal.FreeHGlobal(pDistinguishedName);
       }
   }

   public static IEnumerable<KeyValuePair<string, string>> ParseDN(string distinguishedName)
   {
       List<KeyValuePair<string, string>> components = new List<KeyValuePair<string, string>>();
       IntPtr pDistinguishedName = Marshal.StringToHGlobalUni(distinguishedName);
       try
       {
           IntPtr pDN = pDistinguishedName, pKey, pVal;
           int cDN = distinguishedName.Length, cKey, cVal;

           do
           {
               int lastError = DsGetRdnW(ref pDN, ref cDN, out pKey, out cKey, out pVal, out cVal);

               if(lastError == ERROR_SUCCESS)
               {
                   string key, value;

                   if(cKey < 0)
                   {
                       key = null;
                   }
                   else if(cKey == 0)
                   {
                       key = string.Empty;
                   }
                   else
                   {
                       key = Marshal.PtrToStringUni(pKey, cKey);
                   }

                   if(cVal < 0)
                   {
                       value = null;
                   }
                   else if(cVal == 0)
                   {
                       value = string.Empty;
                   }
                   else
                   {
                       value = Marshal.PtrToStringUni(pVal, cVal);
                   }

                   components.Add(new KeyValuePair<string, string>(key, value));

                   pDN = (IntPtr)(pDN.ToInt64() + UnicodeEncoding.CharSize); //skip over comma
                   cDN--;
               }
               else
               {
                   throw new Win32Exception(lastError);
               }
           } while(cDN > 0);

           return components;
       }
       finally
       {
           Marshal.FreeHGlobal(pDistinguishedName);
       }
   }

   [DllImport("ntdsapi.dll", CharSet = CharSet.Unicode)]
   protected static extern int DsQuoteRdnValueW(
       int cUnquotedRdnValueLength,
       string psUnquotedRdnValue,
       ref int pcQuotedRdnValueLength,
       IntPtr psQuotedRdnValue
   );

   public static string QuoteRDN(string rdn)
   {
       if (rdn == null) return null;

       int initialLength = rdn.Length;
       int quotedLength = 0;
       IntPtr pQuotedRDN = IntPtr.Zero;

       int lastError = DsQuoteRdnValueW(initialLength, rdn, ref quotedLength, pQuotedRDN);

       switch (lastError)
       {
           case ERROR_SUCCESS:
               {
                   return string.Empty;
               }
           case ERROR_BUFFER_OVERFLOW:
               {
                   break; //continue
               }
           default:
               {
                   throw new Win32Exception(lastError);
               }
       }

       pQuotedRDN = Marshal.AllocHGlobal(quotedLength * UnicodeEncoding.CharSize);

       try
       {
           lastError = DsQuoteRdnValueW(initialLength, rdn, ref quotedLength, pQuotedRDN);

           switch(lastError)
           {
               case ERROR_SUCCESS:
                   {
                       return Marshal.PtrToStringUni(pQuotedRDN, quotedLength);
                   }
               default:
                   {
                       throw new Win32Exception(lastError);
                   }
           }
       }
       finally
       {
           if(pQuotedRDN != IntPtr.Zero)
           {
               Marshal.FreeHGlobal(pQuotedRDN);
           }
       }
   }


   [DllImport("ntdsapi.dll", CharSet = CharSet.Unicode)]
   protected static extern int DsUnquoteRdnValueW(
       int cQuotedRdnValueLength,
       string psQuotedRdnValue,
       ref int pcUnquotedRdnValueLength,
       IntPtr psUnquotedRdnValue
   );

   public static string UnquoteRDN(string rdn)
   {
       if (rdn == null) return null;

       int initialLength = rdn.Length;
       int unquotedLength = 0;
       IntPtr pUnquotedRDN = IntPtr.Zero;

       int lastError = DsUnquoteRdnValueW(initialLength, rdn, ref unquotedLength, pUnquotedRDN);

       switch (lastError)
       {
           case ERROR_SUCCESS:
               {
                   return string.Empty;
               }
           case ERROR_BUFFER_OVERFLOW:
               {
                   break; //continue
               }
           default:
               {
                   throw new Win32Exception(lastError);
               }
       }

       pUnquotedRDN = Marshal.AllocHGlobal(unquotedLength * UnicodeEncoding.CharSize);

       try
       {
           lastError = DsUnquoteRdnValueW(initialLength, rdn, ref unquotedLength, pUnquotedRDN);

           switch(lastError)
           {
               case ERROR_SUCCESS:
                   {
                       return Marshal.PtrToStringUni(pUnquotedRDN, unquotedLength);
                   }
               default:
                   {
                       throw new Win32Exception(lastError);
                   }
           }
       }
       finally
       {
           if(pUnquotedRDN != IntPtr.Zero)
           {
               Marshal.FreeHGlobal(pUnquotedRDN);
           }
       }
   }
   #endregion DN Parsing
}

public class DNComponent
{
   public string Type { get; protected set; }
   public string EscapedValue { get; protected set; }
   public string UnescapedValue { get; protected set; }
   public string WholeComponent { get; protected set; }

   public DNComponent(string component, bool isEscaped)
   {
       string[] tokens = component.Split(new char[] { '=' }, 2);
       setup(tokens[0], tokens[1], isEscaped);
   }

   public DNComponent(string key, string value, bool isEscaped)
   {
       setup(key, value, isEscaped);
   }

   private void setup(string key, string value, bool isEscaped)
   {
       Type = key;

       if(isEscaped)
       {
           EscapedValue = value;
           UnescapedValue = Win32LDAP.UnquoteRDN(value);
       }
       else
       {
           EscapedValue = Win32LDAP.QuoteRDN(value);
           UnescapedValue = value;
       }

       WholeComponent = Type + "=" + EscapedValue;
   }

   public override bool Equals(object obj)
   {
       if (obj is DNComponent)
       {
           DNComponent dnObj = (DNComponent)obj;
           return dnObj.WholeComponent.Equals(this.WholeComponent, StringComparison.CurrentCultureIgnoreCase);
       }
       return base.Equals(obj);
   }

   public override int GetHashCode()
   {
       return WholeComponent.GetHashCode();
   }
}

public class DistinguishedName
{
   public DNComponent[] Components
   {
       get
       {
           return components.ToArray();
       }
   }

   private List<DNComponent> components;
   private string cachedDN;

   public DistinguishedName(string distinguishedName)
   {
       cachedDN = distinguishedName;
       components = new List<DNComponent>();
       foreach (KeyValuePair<string, string> kvp in Win32LDAP.ParseDN(distinguishedName))
       {
           components.Add(new DNComponent(kvp.Key, kvp.Value, true));
       }
   }

   public DistinguishedName(IEnumerable<DNComponent> dnComponents)
   {
       components = new List<DNComponent>(dnComponents);
       cachedDN = GetWholePath(",");
   }

   public bool Contains(DNComponent dnComponent)
   {
       return components.Contains(dnComponent);
   }

   public string GetDNSDomainName()
   {
       List<string> dcs = new List<string>();
       foreach (DNComponent dnc in components)
       {
           if(dnc.Type.Equals("DC", StringComparison.CurrentCultureIgnoreCase))
           {
               dcs.Add(dnc.UnescapedValue);
           }
       }
       return string.Join(".", dcs.ToArray());
   }

   public string GetDomainDN()
   {
       List<string> dcs = new List<string>();
       foreach (DNComponent dnc in components)
       {
           if(dnc.Type.Equals("DC", StringComparison.CurrentCultureIgnoreCase))
           {
               dcs.Add(dnc.WholeComponent);
           }
       }
       return string.Join(",", dcs.ToArray());
   }

   public string GetWholePath()
   {
       return GetWholePath(",");
   }

   public string GetWholePath(string separator)
   {
       List<string> parts = new List<string>();
       foreach (DNComponent component in components)
       {
           parts.Add(component.WholeComponent);
       }
       return string.Join(separator, parts.ToArray());
   }

   public DistinguishedName GetParent()
   {
       if(components.Count == 1)
       {
           return null;
       }
       List<DNComponent> tempList = new List<DNComponent>(components);
       tempList.RemoveAt(0);
       return new DistinguishedName(tempList);
   }

   public override bool Equals(object obj)
   {
       if(obj is DistinguishedName)
       {
           DistinguishedName objDN = (DistinguishedName)obj;
           if (this.Components.Length == objDN.Components.Length)
           {
               for (int i = 0; i < this.Components.Length; i++)
               {
                   if (!this.Components[i].Equals(objDN.Components[i]))
                   {
                       return false;
                   }
               }
               return true;
           }
           return false;
       }
       return base.Equals(obj);
   }

   public override int GetHashCode()
   {
       return cachedDN.GetHashCode();
   }
}

Solution 4 - C#

this extension needs less resources than regualr expressions.

public static int CountSubstring(this string text, string value)
{                  
    int count = 0, minIndex = text.IndexOf(value, 0);
    while (minIndex != -1)
    {
        minIndex = text.IndexOf(value, minIndex + value.Length);
        count++;
    }
    return count;
}

usage:

MyString = "OU=Level3,OU=Level2,OU=Level1,DC=domain,DC=com";
int count = MyString.CountSubstring("OU=");

Solution 5 - C#

below should work

  MyString = "OU=Level3,OU=Level2,OU=Level1,DC=domain,DC=com";
  int count = Regex.Matches(MyString, "OU=").Count

Solution 6 - C#

int count = myString.Split(new []{','})
                    .Count(item => item.StartsWith(
                        "OU=", StringComparison.OrdinalIgnoreCase))

Solution 7 - C#

Here are two examples of how you can get the results that you are looking for

var MyString = "OU=Level3,OU=Level2,OU=Level1,DC=domain,DC=com";

This one you would see a list of the values separated but it would have DC just an idea to show that the split with String does work`

var split = MyString.Split(new string[] { "OU=", "," }, StringSplitOptions.RemoveEmptyEntries);

This one will Split and return you only the 3 items into a List so that if you don't rely on a count you can visually validate that it returns the 3 Levels of `OU=``

var lstSplit = MyString.Split(new[] { ',' })
        .Where(splitItem => splitItem.StartsWith(
               "OU=", StringComparison.OrdinalIgnoreCase)).ToList();

Solution 8 - C#

public static int CountOccurences(string needle, string haystack)
{
	return (haystack.Length - haystack.Replace(needle, "").Length) / needle.Length;
}

Benchmarked it against other answers here (the regex one and the "IndexOf" one), works faster.

Content Type	Original Author	Original Content on Stackoverflow
Question	KentZhou	View Question on Stackoverflow
Solution 1 - C#	tnw	View Answer on Stackoverflow
Solution 2 - C#	Jim Mischel	View Answer on Stackoverflow
Solution 3 - C#	JerKimball	View Answer on Stackoverflow
Solution 4 - C#	fubo	View Answer on Stackoverflow
Solution 5 - C#	apollosoftware.org	View Answer on Stackoverflow
Solution 6 - C#	Phil	View Answer on Stackoverflow
Solution 7 - C#	MethodMan	View Answer on Stackoverflow
Solution 8 - C#	Serge Shultz	View Answer on Stackoverflow