I have a list like:
List<String> test = new List<String> {"Luke", "Leia"};
I would like to use something like this:
test.Select(s => String.Format("Hello {0}", s));
but it doesn't adjust the names in the list. Is there a way to use lambda expressions to alter these? Or is it because strings are immutable that this doesn't work?
Select doesn't modify the original collection; it creates a new IEnumerable<T> that you can enumerate with a foreach or convert to a list:
List<String> test2 = test.Select(s => String.Format("Hello {0}", s)).ToList();
test still contains "Luke" and "Leia", and test2 contains "Hello Luke" and "Hello Leia".
If you want to modify the original list with a lambda expression, you can apply the lambda expression to each list item individually and store the result back in the collection:
Func<string, string> f = s => String.Format("Hello {0}", s);
for (int i = 0; i < test.Count; i++)
{
test[i] = f(test[i]);
}
Here:
for(int i = 0; i < test.Count; i++) {
test[i] = String.Format("Hello {0}", test[i]);
}
No need to be fancy. No need to abuse LINQ. Just keep it simple.
You could go one step beyond this and create an extension method like so:
static class ListExtensions {
public static void AlterList<T>(this List<T> list, Func<T, T> selector) {
for(int index = 0; index < list.Count; index++) {
list[index] = selector(list[index]);
}
}
}
Usage:
test.AlterList(s => String.Format("Hello {0}", s));
Select is for projecting and is really intended to be used in circumstances where there are no side-effects. Manipulating the items in the list very clearly has side-effects. In fact, the line
test.Select(s => String.Format("Hello {0}", s));
doesn't do anything except creating an IEnumerable<string> that could eventually be enumerated over to produce the projection.
Select is not meant to be used for causing side effects.Select. Trying to fenagle Select to modify the list would be an abuse of LINQ. As for using lambda expressions, I have provided an extension method that does the job.Select, but looking back over his question I see that he was indeed trying to modify the list he had.One other possible solution:
List<String> test = new List<String> {"Luke", "Leia"};
List<string> FormattedStrings = new List<string>();
test.ForEach(testVal => FormattedStrings.Add(String.Format("Hello {0}", testVal)));
You could just do a foreach statement:
test.ForEach(s=>String.Format("Hello {0}", s));
That is if you are trying to just update the names.
Action<T> and does not modify the List<T>
ForEach(s=> s = String.Format("Hello {0}", s))) doesn't do anything as well.