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[ How to verify in a foreach loop whether the element is last in the collection? ]

I have a foreach loop in which I need to verify whether the element is last in the collection I'm iterating on. What I've tried:

foreach (var character in list) // list is of type `string` 
{
    if (character == list.Last())
    {

    }
}

But in this case if I have "la la la" the if statement will execute on a second character.

Question: How to write the if statement so that it will execute when accessing the last element of a sequence?

Answer 1


I would advise iterating using the index rather than the object reference i.e.

for (int i = 0; i <= list.Count-1; i++)
{
    if (i == list.Count-1)
    {
        // so something special with last item
    }
}

Answer 2


foreach (var character in list) // list is of type `string` 
{
    if (character == list[list.Count - 1])
    {

    }
}

Here is a DEMO.

As an alternative, since List implements IEnumerable interface, you can use Enumerable.Last method

Returns the last element of a sequence.

foreach (var character in list) // list is of type `string` 
{
    if (character == list.Last())
    {

    }
}

Here is a DEMO.

Answer 3


Since your list is actually a string, you need to convert it into a list.

var elementList = list.Split(" ");

You can then find the last element.

var lastElement = elementList.LastOrDefault();

Just check using IsNullOrEmpty to handle the case of an empty list.

Answer 4


If you find yourself doing this kind of thing often, you can use an extension method which will let you ask if an element in a sequence is the last item.

This was originally written by Jon Skeet; he called it "Smart Enumerable", and I believe it is part of the MoreLinq Linq Extensions (also by Jon Skeet).

If you do use such a thing, your code would looks something like this:

foreach (var character in list.AsSmartEnumerable()) 
    if (character.IsLast)
        // Do something with character.Value

Here's a slightly modified copy of Jon Skeet's implementation:

/// <summary>
/// Static class to make creation easier. If possible though, use the extension
/// method in SmartEnumerableExt.
/// </summary>

public static class SmartEnumerable
{
    /// <summary> method to make life easier.</summary>
    /// <typeparam name="T">Type of enumerable</typeparam>
    /// <param name="source">Source enumerable</param>
    /// <returns>A new SmartEnumerable of the appropriate type</returns>

    public static SmartEnumerable<T> Create<T>(IEnumerable<T> source)
    {
        return new SmartEnumerable<T>(source);
    }
}

/// <summary>Wrapper methods for SmartEnumerable[T].</summary>

public static class SmartEnumerableExt
{
    /// <summary>Extension method to make life easier.</summary>
    /// <typeparam name="T">Type of enumerable</typeparam>
    /// <param name="source">Source enumerable</param>
    /// <returns>A new SmartEnumerable of the appropriate type</returns>

    public static SmartEnumerable<T> AsSmartEnumerable<T>(this IEnumerable<T> source)
    {
        return new SmartEnumerable<T>(source);
    }
}

/// <summary>
/// Type chaining an IEnumerable&lt;T&gt; to allow the iterating code
/// to detect the first and last entries simply.
/// </summary>
/// <typeparam name="T">Type to iterate over</typeparam>

[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1710:IdentifiersShouldHaveCorrectSuffix", Justification="This is too general to end in 'Collection'")]

public class SmartEnumerable<T>: IEnumerable<SmartEnumerable<T>.Entry>
{
    /// <summary>Enumerable to which we proxy</summary>

    readonly IEnumerable<T> _enumerable;

    /// <summary>Constructor.</summary>
    /// <param name="enumerable">Collection to enumerate. Must not be null.</param>

    public SmartEnumerable(IEnumerable<T> enumerable)
    {
        if (enumerable==null)
        {
            throw new ArgumentNullException("enumerable");
        }

        this._enumerable = enumerable;
    }

    /// <summary>
    /// Returns an enumeration of Entry objects, each of which knows
    /// whether it is the first/last of the enumeration, as well as the
    /// current value.
    /// </summary>

    public IEnumerator<Entry> GetEnumerator()
    {
        using (IEnumerator<T> enumerator = _enumerable.GetEnumerator())
        {
            if (!enumerator.MoveNext())
            {
                yield break;
            }

            bool isFirst = true;
            bool isLast  = false;
            int  index   = 0;

            while (!isLast)
            {
                T current = enumerator.Current;
                isLast = !enumerator.MoveNext();
                yield return new Entry(isFirst, isLast, current, index++);
                isFirst = false;
            }
        }
    }

    /// <summary>Non-generic form of GetEnumerator.</summary>

    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }

    /// <summary>
    /// Represents each entry returned within a collection,
    /// containing the value and whether it is the first and/or
    /// the last entry in the collection's. enumeration
    /// </summary>

    public class Entry
    {
        internal Entry(bool isFirst, bool isLast, T value, int index)
        {
            this._isFirst = isFirst;
            this._isLast  = isLast;
            this._value   = value;
            this._index   = index;
        }

        /// <summary>The value of the entry.</summary>

        public T Value
        {
            get
            {
                return _value;
            }
        }

        /// <summary>Whether or not this entry is first in the collection's enumeration.</summary>

        public bool IsFirst
        {
            get
            {
                return _isFirst;
            }
        }

        /// <summary>Whether or not this entry is last in the collection's enumeration.</summary>

        public bool IsLast
        {
            get
            {
                return _isLast;
            }
        }

        /// <summary>The 0-based index of this entry (i.e. how many entries have been returned before this one)</summary>

        public int Index
        {
            get
            {
                return _index;
            }
        }

        readonly bool _isFirst;
        readonly bool _isLast;
        readonly T    _value;
        readonly int  _index;
    }
}

Answer 5


If you only want to do an action on the last character, then Mare Infinitus' code should do the trick.

What about:

var elementList = list.Split(" ");
if (elementList.Last().Equals(character))
{
   // do something here
}

this should do it, no need for foreach.

However, if you want to loop and do a specific action for the last character, then you can use a standard for loop. James' answer:

for (int i = 0; i <= list.Count-1; i++)
{
    if (i == list.Count-1)
    {
        // so something special with last item
    }
}

Answer 6


If you only have an IEnumerable, you have to manually trigger the enumerator. Here is a sample extension method which maybe helps you:

public static class IEnumerableExtensions
{
    public static void Action<T>(this IEnumerable<T> source, Action<T> sequenceElement, Action<T> lastElement)
    {
        if (source == null)
            throw new ArgumentNullException("source");

        if (sequenceElement == null)
            throw new ArgumentNullException("sequenceElement");

        if (lastElement == null)
            throw new ArgumentNullException("lastElement");

        T element = default(T);

        using (var enumerator = source.GetEnumerator())
        {
            if (enumerator.MoveNext())
                element = enumerator.Current;

            while (enumerator.MoveNext())
            {
                sequenceElement(element);
                element = enumerator.Current;
            }

            lastElement(element);
        }
    }
}

You can then call it this way:

var myElements = Enumerable.Range(1, 10);

myElements.Action(value => Console.WriteLine("Something out of the sequence: " + value),
                    value => Console.WriteLine("The last element: " + value));