Dictionary, Equals

Two Dictionaries are equal if their contents are the same. A Dictionary is a reference type—its bits cannot just be checked.

Two Dictionaries may have different orders of keys, even if they are equal. The counts, and exact contents, of the collections must be tested.

Example code

Two Dictionary instances are allocated upon the managed heap at program runtime. Each Dictionary has 3 key-value pairs. The data is equal in every way.

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Create a dictionary and add several elements to it.
        var dict = new Dictionary<string, int>();
        dict.Add("cat", 2);
        dict.Add("dog", 3);
        dict.Add("x", 4);

        // Create another dictionary.
        var dict2 = new Dictionary<string, int>();
        dict2.Add("cat", 2);
        dict2.Add("dog", 3);
        dict2.Add("x", 4);

        // Test for equality.
        bool equal = false;
        if (dict.Count == dict2.Count) // Require equal count.
        {
            equal = true;
            foreach (var pair in dict)
            {
                int value;
                if (dict2.TryGetValue(pair.Key, out value))
                {
                    // Require value be equal.
                    if (value != pair.Value)
                    {
                        equal = false;
                        break;
                    }
                }
                else
                {
                    // Require key be present.
                    equal = false;
                    break;
                }
            }
        }
        Console.WriteLine(equal);
    }
}
True

Notes, algorithm

The algorithm used has several details. If you do not correctly add every constraint, it will not return correct results. The counts of the 2 dictionaries must be equal.

1. Counts
2. All keys are found
3. All keys have matching values

It is possible to compare two Dictionary instances for equality using a custom method with key-value pair checking. There are other possible implementations.

However, this implementation is resource-efficient and simple. When testing this method, make sure to change keys and values in both dictionaries.