Count the number of frequency for different characters in a string

Question

i am currently tried to create a small program were the user enter a string in a text area, clicks on a button and the program counts the frequency of different characters in the string and shows the result on another text area. E.g. Step 1:- User enter:- aaabbbbbbcccdd Step 2:- User click the button Step 3:- a 3 b 6 c 3 d 1 This is what I've done so far....

    public partial class Form1 : Form
    {
        Dictionary<string, int> dic = new Dictionary<string, int>();
        string s = "";
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {

            s = textBox1.Text;
            int count = 0;
            for (int i = 0; i < s.Length; i++ )
            {
                textBox2.Text = Convert.ToString(s[i]);
                if (dic.Equals(s[i]))
                {
                    count++;
                }
                else
                {
                    dic.Add(Convert.ToString(s[i]), count++);
                }
            }

        }
    }
}

Any ideas or help how can I countinue because till now the program is giving a run time error when there are same charachter!!

Thank You

Valentin Kuzub · Accepted Answer · 2013-11-24 21:22:37Z

2

var lettersAndCounts = s.GroupBy(c=>c).Select(group => new { 
                             Letter= group.Key, 
                             Count = group.Count() 
                        });

answered Nov 24, 2013 at 21:22

Valentin Kuzub

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Comments

Tim Schmelter · Accepted Answer · 2013-11-24 21:23:25Z

1

Instead of dic.Equals use dic.ContainsKey. However, i would use this little linq query:

Dictionary<string, int> dict = textBox1.Text
    .GroupBy(c => c)
    .ToDictionary(g => g.Key.ToString(), g => g.Count());

answered Nov 24, 2013 at 21:23

Tim Schmelter

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2 Comments

user2307236 Over a year ago

I've used the linq query and it is working fine... since I am a beginner can you kindly explain what is happening in the few lines of code.. Tks

Tim Schmelter Over a year ago

@user2307236: It's even only a single line. Enumerable.GroupBy groups each char in the string by it's value, ToDictionary creates a dictionary by a provided key and a value. The key is the Key property of the group which is the char. If you use GroupBy is it ensured that you get no duplicates. The value is the IEnumerable<Char> of same chars. The Enumerable.Count method enumerates these chars to get the total count of each group.

Guffa · Accepted Answer · 2013-11-24 21:36:38Z

0

You are attempting to compare the entire dictionary to a string, that doesn't tell you if there is a key in the dictionary that corresponds to the string. As the dictionary never is equal to the string, your code will always think that it should add a new item even if one already exists, and that is the cause of the runtime error.

Use the ContainsKey method to check if the string exists as a key in the dictionary.

Instead of using a variable count, you would want to increase the numbers in the dictionary, and initialise new items with a count of one:

string key = s[i].ToString();
textBox2.Text = key;
if (dic.ContainsKey(key)) {
  dic[key]++;
} else {
  dic.Add(key, 1);
}

edited Nov 24, 2013 at 21:36

answered Nov 24, 2013 at 21:24

Guffa

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2 Comments

user2307236 Over a year ago

I tried the above however compiler is giving error that I have invalid arguments... I guess the problem is because dic takes two arguments a string and int....

Guffa Over a year ago

@user2307236: Yes, you are right. The value has to be a string everywhere it's used with the dictionary. I updated the code above.

Pepe · Accepted Answer · 2013-11-24 21:21:38Z

0

I'm going to suggest a different and somewhat simpler approach for doing this. Assuming you are using English strings, you can create an array with capacity = 26. Then depending on the character you encounter you would increment the appropriate index in the array. For example, if the character is 'a' increment count at index 0, if the character is 'b' increment the count at index 1, etc...

Your implementation will look something like this:

int count[] = new int [26] {0};

for(int i = 0; i < s.length; i++)
{
   count[Char.ToLower(s[i]) - int('a')]++;
}

When this finishes you will have the number of 'a's in count[0] and the number of 'z's in count[25].

answered Nov 24, 2013 at 21:21

Pepe

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2 Comments

user2307236 Over a year ago

I cannot understand this part of code ..... - int('a')]++ and also {0} can you kindly explain....

Pepe Over a year ago

The {0} initializes all the elements in your count array to 0. int('a') basically returns the ascii code for the character a which is actually 97. So if you encounter 'b' we will increment index 98-97=1! 98 here is the ascii of 'b' and so on. Letter z has ascii 122 and will be placed in index 122-97=25.

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