Handy LINQ & Lambda Methods and Extensions (Part I)

The System.Linq namespace contains a fantastic set of utility extension methods for filtering, ordering & manipulating the contents of your collections and objects. In the following posts I'll go through some of the most useful ones (in my humble opinion) and how you might use them in your C# solutions
[su_note note_color="#dee3ab" text_color="#5E826F"]This is part 1 in a series of posts on Linq & Lambda capabilities in C# [/su_note]

Before we start, here's a handy static method to print your resulting collections to the console so you can quickly verify the results.

public class SuperConsole
{
    public static void WriteLine<T>(IEnumerable<T> list, bool includeCarriageReturnBetweenItems =false)
    {
        var seperator = includeCarriageReturnBetweenItems ? ",\n" : ", ";
        var result = string.Join(seperator, list);
        Console.WriteLine(result);
    }
}

Enumerable

The System.Linq.Enumerable type has 2 very useful static methods on it for quickly generating a sequence of items. Enumerable.Range & Enumerable.Repeat. The Range method allows you to quickly generate a sequential list of integers from a given starting point for a given number of items.

IEnumerable<int> range = Enumerable.Range(1, 10);
SuperConsole.WriteLine(range);
//prints "1, 2, 3, 4, 5, 6, 7, 8, 9, 10"

So why is this useful, well you could use it to quickly generate a pre-initialised list of integers rather than new'ing up a list and then iterating over it to populate it. Or you could use it to replicate for(;;) behavior. e.g.

for (int i = 1; i <= 10; i++) 
{     
    //DoWork(i); 
} 

Enumerable.Range(1, 10).ToList().ForEach(i =>
{
    //DoWork(i)
});

Repeat is similar but is not limited to integers. You can generate a Sequence of a given length with the same default value in every item. Imagine you wanted to create a list of 10 strings all initialised with a default string of "ABC";

var myList = Enumerable.Repeat("ABC", 10).ToList();

Item Conversion

There are also a few handy ways to convert/cast items built into the System.Linq namespace. The Cast<T> extension method allows you to cast a list of variables from one type to another as long as a valid cast is available. This can be useful for quickly changing a collection of super types into their base types.

var integers = Enumerable.Range(1, 5);
var objects = integers.Cast<object>().ToList();

Console.WriteLine(objects.GetType());
SuperConsole.WriteLine(objects);

//prints
//System.Collections.Generic.List`1[System.Object]
//1, 2, 3, 4, 5

But what if a valid implicit cast isn't available. What if we wanted to convert our collection of integers into a collection of strings with a ':' suffix. Thankfully Linq has us covered with it's ConvertAll Method on List

var integers = Enumerable.Range(1, 5);
var converter = new Converter<int, string>(input => string.Format("{0}: ", input));
var results = integers.ToList().ConvertAll(converter);

SuperConsole.WriteLine(results, true);
/*prints
    1:
    2:
    3:
    4:
    5:
    */

In the next post, we'll look at some the lazy & deferred execution capabilities of LINQ and some useful methods for performing quick calculations and manipulations on our collections.

~Eoin Campbell