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C# C# Collections Sets and Dictionaries Using Dictionaries

Alan Mills
Alan Mills
31,712 Points
Posted by Alan Mills
Alan Mills
31,712 Points

"The given key was not present in the dictionary."

Excuse the multiple writing to the console. But, I was trying to confirm that I was searching by the key (string) to obtain (& update) the value.

It feels like I'm accessing and updating the value. But, I don't understand what I need to fix.

Thanks!

LexicalAnalysis.cs 
using System;
using System.Collections.Generic;

namespace Treehouse.CodeChallenges
{
    public class LexicalAnalysis
    {
        public Dictionary<string, int> WordCount = new Dictionary<string, int>();

        public void AddWord(string word)
        {
            int newCount = WordCount[word] + 1;
            Console.Write(word);
            Console.Write(WordCount[word]);

            if(WordCount.ContainsKey(word))
            {
                WordCount[word] = newCount;
                Console.Write(WordCount[word]);

                // WordCount[word] = newCount;
            }

        }
    }
}

3 Answers

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

You probably don't want to create "newCount" until after you check that the word exists in the dictionary. If not, trying to access the current value causes the error you are seeing.

Then, if the value does not already exist you'll want to add a new item with a value of 1.

Alan Mills
Alan Mills
31,712 Points
Alan Mills
Alan Mills
31,712 Points

Ahhhhhh. Didn’t think of that! Will try it when I have a moment. Thanks!

Alan Mills
Alan Mills
31,712 Points
Alan Mills
Alan Mills
31,712 Points

Unfortunately, this didn't solve it. But I also figured it would. I'm somehow not actually accessing the dictionary keys. Same error prompt. I think it's in the if statement...

====================== using System.Collections.Generic; using System;

namespace Treehouse.CodeChallenges { public class LexicalAnalysis { public Dictionary<string, int> WordCount = new Dictionary<string, int>();

    public void AddWord(string word)
    {
        int newCount = 0;
        if (WordCount.ContainsKey(word))
        {
            newCount = WordCount[word] + 1;
            WordCount[word] = newCount;
        }
        WordCount.Add(word, newCount);

        Console.WriteLine(WordCount[word]);   
        Console.WriteLine(word);

    }
}

}

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

You won't need to add an item again if it exists. But if the value does not already exist you still need to add a new item with a value of 1. So you probably need an "else" to go with the "if".