Number of occurrences of a character in a string and their positions

Question

Console.WriteLine("Insert the character you are searching for: ");
CharacterSearch = Console.ReadLine();
var count = file.Where(x => x == CharacterSearch).Count();

So what I am trying to do is to read text from the variable file and then search for a specific character in the string that is entered from the keyboard. So the searched character would be CharacterSearch.

I also want to check for their positions not just the number of occurrences.

forgot to say that this does not show the number of aparitions because i get the error "Operator == cannot be used for Strings or Char". — xDevil, Dec 06 '13 at 14:47
First off [How would you count occurrences of a string within a string?](http://stackoverflow.com/questions/541954/how-would-you-count-occurrences-of-a-string-within-a-string) — Liam, Dec 06 '13 at 14:48
Just get the first character from the input string, or do a ReadKey instead of a ReadLine — Panagiotis Kanavos, Dec 06 '13 at 14:59

Mike Perrenoud · Answer 1 · 2013-12-06T15:28:51.880

1

This is very inefficient, but it's an option is the files are small.

CharacterSearch = Console.ReadKey();
var count = File.ReadLines(pathToFile)
    .Select((c, i) => new { Character = c, Index = i })
    .ToList()
    .Where(x => x.Character == CharacterSearch);

edited Dec 06 '13 at 15:28

answered Dec 06 '13 at 14:47

Mike Perrenoud

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i get the error Char does not contain a definition of KeyChar – xDevil Dec 06 '13 at 15:05
Now i get the error : System.IO.StreamReader does not contain a definition of select.Keep in mind im trying to search through a text file.:( – xDevil Dec 06 '13 at 15:25
@user2524603, please see my edit, and get rid of that `StreamReader`. – Mike Perrenoud Dec 06 '13 at 15:29
Now i get no errors but the program just does nothing after this point. – xDevil Dec 06 '13 at 15:38
This is the file code! might have something to do with it. Console.WriteLine(Extra); int counter = 0; string line; System.IO.StreamReader file = new System.IO.StreamReader(PathS); while ((line = file.ReadLine()) != null) { Console.WriteLine(line); counter++; } – xDevil Dec 06 '13 at 15:39
@user2524603, well you've got to do something with the results. It's a `List` where `T` is the anonymous type created there. – Mike Perrenoud Dec 06 '13 at 15:39
@user2524603, get *rid of the `StreamReader`!* The `File.ReadLines` does *all the work.* – Mike Perrenoud Dec 06 '13 at 15:40

score 1 · Answer 2 · answered Dec 06 '13 at 14:50

1

Why not simply use this method? (Are you looking for a complicated one?)

List<int> indexes = new List<int>();

for (int i = 0; i < file.Length; i++)
{
    if (file[i]==CharacterSearch)
    {
        indexes.Add(i);    
    }
}

int count = indexes.Count;

answered Dec 06 '13 at 14:50

Hossein Narimani Rad

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file[i] == CharacterSearch line has the same error i had before that operator == cannot be used for Char and String – xDevil Dec 06 '13 at 14:57
1

@user2524603 Because you need `char CharacterSearch = Console.ReadKey().KeyChar;` – Matthew Watson Dec 06 '13 at 14:58

score 0 · Answer 3 · answered Dec 06 '13 at 15:10

Inefficient but can be applied if file is small.

public static int CharCount(string input,char c)
{
    var charCount=input.GroupBy(a => a).ToDictionary(k => k.Key, v => v.Count());
    if (charCount.ContainsKey(c))
        return charCount[c];
    return 0;
}

If you want to do the search over an over in the same string, i think it is better maintain a mapping. Again considerable only for a small file.

 public static Dictionary<char, int> CharCountMapping(string input)
{
    return input.GroupBy(a => a).ToDictionary(k => k.Key, v => v.Count());
}

Number of occurrences of a character in a string and their positions

3 Answers3