Let’s continue to explore the List data type methods! I’ll also present a particularly useful string method that you’ll want to port to RPG.
The last TechTip introduced the List data type and explained a few of its (many) methods. This one will pick up where the last one left off. If you read the previous article, you’ll know that there’s an intruder in the list of IBM i names: “S/38” should be removed. Let’s start there.
Two Ways to Remove Stuff from a List
Fire up Visual Studio and open the IntroducingLists.sln project. Once it loads, position the cursor after the last line of code of the Main method and you’re ready to start.
Removing an element from a List can be performed in two ways: you need to know either the contents of the element you want to remove or in which position of the List the element is. Let’s start with the first option, which is simpler, in this case, because it’s a string. My serverNames variable is a List of strings, so I can use the actual string I’m looking for (“S/38”) as a parameter to the Remove method:
I know that “S/38” was in position 0 because it was the first element I added (remember, Lists, just like Arrays, use a zero-based positional notation). But let’s imagine for a minute that I didn’t know where it was. How could I find out? If you’re saying something like “I’m sure there’s a method for that!” you’re correct: it’s the IndexOf method. This method returns, as the name implies, the index (or position) of an element in a List. In order to test it, let’s re-add the “S/38” string to our list of server names and, after that, output the position of the string on the list:
Console.WriteLine("S/38 now exists on position " +
If you type this and run the program, the output should show “S/38 now exists on position 3”, among other things. Good, so now I can use the other method to remove elements from a List. This method is called RemoveAt, and it works like this:
Naturally, you can combine multiple methods on the same expression, just like you’d do in RPG. I can combine the IndexOf and RemoveAt methods on the same instruction because the CLR (that’s the Common Language Runtime – more information about it here) is intelligent enough to evaluate the result of each in the correct order (starting on the innermost method and making its way to the outermost one) to produce the appropriate result. Here’s how it could look:
However, if you run your program with this line of code, it won’t remove anything, because “S/38” no longer exists on the list. How can you check? With the Contains method. Here’s an example:
Console.WriteLine("It's " + serverNames.Contains("S/38") + " that the list contains S/38");
Naturally, you can also output the entire list and visually check if the “S/38” element is there. Let’s try that. But if you’re thinking about using a foreach loop, think again…
A String Surprise
Instead of a “classic” foreach loop, I’ll use a very nice method from the string class. You probably remember from a couple of TechTips ago that there are some methods that exist not on the variables that you create, but on the class that defines those objects. I explained this using the Array.Sort method to sort an array of integers. This time around, I’ll use a string method to output a nicely formatted list of values formed by the elements of our serverNames list. This method is very simple to use, and I’m tempted to create an RPG function that mimics its behavior. Anyway, the following line of code produces a list of comma-separated strings:
Console.WriteLine(string.Join(", ", serverNames));
I’m using the by-now-familiar Console.WriteLine method to send something to the screen. That something is the result of the call to the string.Join method. This method has two parameters: a separator string (it can be a single character or something else) and a list of values, which doesn’t necessarily have to be a list of strings. Naturally, it must be something that is convertible to string—otherwise, it won’t produce a proper output—but it can be a list of numbers, for instance. You can find the full documentation and additional examples of this method here.
There’s a Name Missing
If you’ve been typing along and you ran the latest version of the code, you probably noticed that there’s still something missing, from a historical point of view: I “forgot” to include the “System i” name between “iSeries” and “IBM i”. In other words, I need to insert “System i” in position 2 of the list. How do I do that? Well, naturally, there’s a method for it. It’s called (you guessed it) Insert.
serverNames.Insert(2, "System i");
The code should be self-explanatory, but I’ll explain it anyway: The first parameter of this method indicates the position on which the second parameter will be inserted. Its simplicity is yet another argument in favor of using Lists instead of Arrays.
That’s all the space I have this time around! Next time, I’ll discuss a few more methods to reverse, sort, and remove duplicates from a List. In the meantime, please speak your mind in the Comments section. Your feedback is a precious way to improve this TechTip series!