FindLast on IEnumarable

Question

I would like to call FindLast on a collection which implements IEnumarable, but FindLast is only available for List. What is the best solution?

Answer 1

Use the extension method Last() which is located in the namespace System.Linq.

Answer 2

you can add you collection to a new List by passing it to List<> constructor.

List<MyClass> myList = new List<MyClass>(MyCol);
myList.FindLast....

Answer 3

The equivalent to:

var last = list.FindLast(predicate);

is

var last = sequence.Where(predicate).LastOrDefault();

(The latter will have to check all items in the sequence, however...)

Effectively the "Where()" is the Find part, and the "Last()" is the Last part of "FindLast" respectively. Similarly, FindFirst(predicate) would be map to sequence.Where(predicate).FirstOrDefault() and FindAll(predicate) would be sequence.Where(predicate).

Answer 4

How about with LINQ-to-Objects:

var item = data.LastOrDefault(x=>x.Whatever == "abc"); // etc

If you only have C# 2, you can use a utility method instead:

using System;
using System.Collections.Generic;
static class Program {
    static void Main() {
        int[] data = { 1, 2, 3, 4, 5, 6 };

        int lastOdd = SequenceUtil.Last<int>(
            data, delegate(int i) { return (i % 2) == 1; });
    }    
}
static class SequenceUtil {
    public static T Last<T>(IEnumerable<T> data, Predicate<T> predicate) {
        T last = default(T);
        foreach (T item in data) {
            if (predicate(item)) last = item;
        }
        return last;
    }
}

Answer 5

Your question is invalid because a collection has no last element. A more specialized collection that does have a complete ordering is a list. A more specialized collection that does not have an ordering is a dictionary.