C# Get value from dictionary

using System;
using System.Collections.Generic;

var studentGrades = new Dictionary<string, double>()
{
    ["Alice"] = 85.5,
    ["Bob"] = 92.0,
    ["Charlie"] = 78.3
};

// Get grade by key using indexer
var grade = studentGrades["Bob"];
Console.WriteLine($"Bob's grade: {grade}");

Output: Bob's grade: 92

Note: If the key doesn’t exist, this will throw a KeyNotFoundException.

Get the value if the key exists

Use Dictionary.TryGetValue() to avoid exceptions. If the key exists, it returns true and provides the value; otherwise, it returns false.

if (studentGrades.TryGetValue("Charlie", out double grade))
{
    Console.WriteLine($"Charlie's grade: {grade}");
}
else
{
    Console.WriteLine("Charlie's grade not found.");
}

Output: Charlie's grade: 78.3

If the key doesn’t exist, the out parameter remains the type’s default value (e.g., 0.0 for double).

Use ContainsKey() and Indexer

TryGetValue() is a shortcut, but you can also combine ContainsKey() with the indexer:

if (studentGrades.ContainsKey("Alice"))
{
    var grade = studentGrades["Alice"];
    Console.WriteLine($"Alice's grade: {grade}");
}

Output: Alice's grade: 85.5

Get the value or default if the key doesn’t exist

To handle missing keys more elegantly, use Dictionary.GetValueOrDefault(). It returns the value if the key exists or a default value otherwise.

// Get grade for existing student
var aliceGrade = studentGrades.GetValueOrDefault("Alice");
Console.WriteLine($"Alice's grade: {aliceGrade}");

// Get grade for a non-existent student
var unknownGrade = studentGrades.GetValueOrDefault("Eve", -1.0);
Console.WriteLine($"Eve's grade: {unknownGrade}");

Output:

Alice's grade: 85.5  
Eve's grade: -1

Get all values in the dictionary

Sometimes, you might need to process all values in the dictionary. Use Dictionary.Values to get all values.

using System.Linq;

var grades = studentGrades.Values;

// Total number of grades
Console.WriteLine($"Total grades: {grades.Count}");

// Count grades above 80
var countAbove80 = grades.Where(g => g > 80).Count();
Console.WriteLine($"Number of grades above 80: {countAbove80}");

Output:

Total grades: 3  
Number of grades above 80: 2