在列表中添加值<ienumerable<t> &gt; 内部 foreach </ienumerable<t>

Question

what I want to do is to add for example class in IEnumerable after specific check

public static IEnumerable<T> GroupBy<T, O> (this IEnumerable<T> list, Func<T, O> filter)
    {
        List<IEnumerable<T>> grouped = new List<IEnumerable<T>>();

        foreach (var item in list)
        {
            foreach (var g in grouped)
            {
                foreach (var p in g)
                {
                    if (filter(p).Equals(filter(item)))
                    {
                        // Add item to g
                    }
                }
            }
        }
    }

Is something like this possible in foreach?

Answer 1

No, that's not possible: every time you change source collection, foreach has to be started anew. You'll need to have a separate collection for intermediate accumulation, then join that collection with grouped .

Also, your algorithms doesn't work correctly: the second foreach will never start working as on the first iteration there will be no items in grouped collection. So you will just iterate list without applying any logic to its elements.