Number of occurrences of a character in a string

Question

I am trying to get the number of occurrences of a certain character such as  amp  in the following string   string test    key1 value1 amp key2 value2 amp key3 value3     How do I determine that there are 2 ampersands   amp   in the above test string variable

User · Answer

Because LINQ can do everything      string test    key1 value1 amp key2 value2 amp key3 value3   var count   test Where x   gt  x      amp    Count      Or if you like  you can use the Count overload that takes a predicate    var count   test Count x   gt  x      amp

User · Answer

You could do this   int count   test Split   amp    Length - 1    Or with LINQ   test Count x   gt  x      amp

User · Answer

Here is the most inefficient way to get the count in all answers  But you ll get a Dictionary that contains key-value pairs as a bonus   string test    key1 value1 amp key2 value2 amp key3 value3    var keyValues   Regex Matches test       w d       w d     amp                             Cast lt Match gt                          ToDictionary m   gt  m Groups 1  Value  m   gt  m Groups 2  Value    var count   keyValues Count - 1

User · Answer

Your string example looks like the query string part of a GET  If so  note that HttpContext has some help for you  int numberOfArgs   HttpContext Current QueryString Count    For more of what you can do with QueryString  see NameValueCollection

User · Answer

Why use regex for that  String implements IEnumerable lt char gt   so you can just use LINQ    test Count c   gt  c      amp

User · Answer

The most straight forward  and most efficient  would be to simply loop through the characters in the string   int cnt   0  foreach  char c in test      if  c      amp    cnt        You can use Linq extensions to make a simpler  and almost as efficient version  There is a bit more overhead  but it s still surprisingly close to the loop in performance   int cnt   test Count c   gt  c      amp       Then there is the old Replace trick  however that is better suited for languages where looping is awkward  SQL  or slow  VBScript    int cnt   test Length - test Replace   amp        Length

[c#] Number of occurrences of a character in a string

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