Custom extension methods on IEnumerable<T>

Question

In my project we are getting different list and array of elements and need to pick alternative for those list and array for example if my list consist of

string[] toys= { "car", "bat-mask", "halloween-toys", "marvel-toys", "transformer" };

now it may be a list of hundreds of elements my problems is to choose alternative from above list like if i have configuratioin to pick one after another ie car after that skip bat-mask and pick halloween-toys this is my first priority and after that i make it configurable like how many item to skip in between like one item or two items etc.

Reason to use it as extension because it will be use inside complete app and i simply need it access like var myList = toys.customExtensionMethods();

Answer 1

You can use that:

using System.Linq;

static public class IEnumerableHelper
{
  static public IEnumerable<T> customExtensionMethods<T>(this IEnumerable<T> items, 
                                                         T takeFirst, 
                                                         int skipCount)
  {
    var list1 = items.SkipWhile(item => !item.Equals(takeFirst));
    var list2 = list1.Skip(skipCount + 1).Take(1);
    return list1.Take(1).Concat(list2);
  }
}

Test 1

static void Test()
{
  string[] toys = { "car", "bat-mask", "halloween-toys", "marvel-toys", "transformer" };
  var list = toys.customExtensionMethods("car", 1);
  foreach ( var item in list )
    Console.WriteLine(item);
}

Output:

car
halloween-toys

Test 2

var list = toys.customExtensionMethods("bat-mask", 2);

Output

bat-mask
transformer

Answer 2

If i am not wrong, inside your extension method you want to get array element with no Of skip value passed.

   public static class ExtensionMethod
    {
        public static string[] CustomExtensionMethods(this string[] myData, int NoofSkip)
        {
            var newData = new List<string>();
            for (int i = 0; i < myData.Length; i++ )
            {
                newData.Add(myData[i]);
                i = i + NoofSkip;
            }

            return newData.ToArray();
        }
    }

Call Method:

var data = toys.CustomExtensionMethods(1);

OutPut:

 { "car", "halloween-toys", "transformer" };

Answer 3

I hope I understood your question correctly. You are intending to create an extension method which takes an input 'searchterm' and a count skip count. The method searches for the item in the list, skips the next n items and returns the new item. You could do as the following.

public static class Extensions
{
    public static T PickAlternative<T>(this IEnumerable<T> source,string item,int skipCount)
    {
        return source.SkipWhile(x=> !x.Equals(item)).Skip(skipCount).First();
    }
}

Example,

toys.PickAlternative("bat-mask",3);
toys.PickAlternative("car",2);

Output

transformer
halloween-toys

Answer 4

public static class EnumerableExtensions
{
    public static IEnumerable<T> PickAlternate<T>(this IEnumerable<T> source, int skip)
    {
        int? currentlySkipped = null;

        foreach (var item in source)
        {
            if (!currentlySkipped.HasValue || currentlySkipped == skip)
            {
                currentlySkipped = 0;
                yield return item;
            }
            else
            {
                currentlySkipped++;
            }


         }
    }
}