Count, Dictionary

A Dictionary contains a certain number of keys and values. This number is returned by the Count property. No looping is usually needed.

With Count we quickly determine how much data is stored in the Dictionary. The field is stored as elements are added, so it is fast to access.

Example

The Count property returns the number of keys. This count integer is not equal to the Dictionary fill rate or its internal bucket count.

using System;
using System.Collections.Generic;

// Create new Dictionary with 4 keys.
Dictionary<string, int> dictionary = new Dictionary<string, int>();
dictionary.Add("carrot", 1);
dictionary.Add("pear", 4);
dictionary.Add("apple", 6);
dictionary.Add("kiwi", 3);

// Count the keys.
int count1 = dictionary.Count;

// Remove one key.
dictionary.Remove("pear");

// Count the keys again.
int count2 = dictionary.Count;

// Clear the Dictionary contents.
dictionary.Clear();

// Count the keys again.
int count3 = dictionary.Count;

// Write the counts of the Dictionary.
Console.WriteLine(count1);
Console.WriteLine(count2);
Console.WriteLine(count3);
4
3
0

Implementation

Count is implemented as a property accessor—it is not a direct field access. Instead, the call to Count does a simple and fast calculation each time you call it.

public int Count
{
    get
    {
        return (this.count - this.freeCount);
    }
}

Limitations

The Count property gives you no insight into the internal implementation state of the Dictionary. For detailed performance analysis, a debugger can be used.

Condition

The Count property cannot be used to filter or selectively count keys. For this purpose, we can use a foreach-loop over the Keys property, with an if-conditional.

We can get the number of keys and values in a Dictionary. Because the Dictionary enforces unique keys, you can use Count to compute the number of unique keys in a collection.