How to Convert all strings in List<string> to lower case using LINQ?

Question

Hi all,

I saw a code snippet yesterday in one of the responses here on StackOverflow that intrigued me. It was something like this:

 List<string> myList = new List<string> {"aBc", "HELLO", "GoodBye"};

 myList.ForEach(d=>d.ToLower());

I was hoping I could use it to convert all items in myList to lowercase. However, it doesn't happen... after running this, the casing in myList is unchanged.

So my question is whether there IS a way, using LINQ and Lambda expressions to easily iterate through and modify the contents of a list in a manner similar to this.

Thanks, Max

Answer 1

[TestMethod]
public void LinqStringTest()
{
    List<string> myList = new List<string> { "aBc", "HELLO", "GoodBye" };
    myList = (from s in myList select s.ToLower()).ToList();
    Assert.AreEqual(myList[0], "abc");
    Assert.AreEqual(myList[1], "hello");
    Assert.AreEqual(myList[2], "goodbye");
}

Answer 2

That's because ToLower returns a lowercase string rather than converting the original string. So you'd want something like this:

List<string> lowerCase = myList.Select(x => x.ToLower()).ToList();

Answer 3

ForEach uses Action<T>, which means that you could affect x if it were not immutable. Since x is a string, it is immutable, so nothing you do to it in the lambda will change its properties. Kyralessa's solution is your best option unless you want to implement your own extension method that allows you to return a replacement value.

Answer 4

Easiest approach:

myList = myList.ConvertAll(d => d.ToLower());

Not too much different than your example code - just a re-assignment and different extension method.