Convert a foreach loop to LINQ in C# – Code Example

We can convert a foreach loop to LINQ in C# using defined syntax of linq. The Linq query works when there is IEnumerable in foreach loop.

Suppose you have a c# foreach loop using IEnumerable –

public void loopMethod() {

  List<string> superheroes = new List<string>() {"Ironman", "Hulk", "Superman", "Flash"};

  IEnumerable<string> enumerable()
  {
    foreach (var superhero in superheroes)
    {
       yield return superhero;
    }

    yield break;
  } 
}

We can convert it into LINQ syntax, like this –

public void loopMethod() {

  List<string> superheroes = new List<string>() {"Ironman", "Hulk", "Superman", "Flash"};

  IEnumerable<string> enumerable()
  {
    return from string superhero in superheroes
           select superhero;
  } 
}

In more generic form, you can use this –

// Generic List 👇
List<T> listName = new List<T>() {... list items ...};

// Foreach Syntax 👇
foreach(var singleItem in listName) yield return singleItem;

// LINQ Syntax 👇
return from T singleItem in listName select singleItem;

We can also use conditions in LINQ. For example, if there is a condition in foreach for only returning the strings of length > 5 then, linq uses where keyword with condition.

// Foreach with condition 👇
foreach (var superhero in superheroes)
{
    if(superhero.length > 5)
        yield return superhero;
}

// LINQ with where 👇
return from string superhero in superheroes
       where superhero.length > 5
       select superhero;

We can also use the linq call form which is slightly different. Here it is –

// linq call form 👇
return superheroes
       .Where(superhero => superhero.length > 5)
       .Select(superhero => superhero);