Adding IEnumerable items to IEnumerable

Question

I have the following:

 foreach (var item in selected)
 {
    var categories = _repo.GetAllDCategories(item);
    var result = from cat in categories
                 select
                     new
                     {
                        label = cat.Name,
                        value = cat.Id
                     };
}

The method GetAllDCategories returns a IEnumerable<T>

How to add result to new IEnumerable object that will contain all the items from result for all the selected items in the loop?

You can't add anything to an existing `IEnumerable`-> it is a read-only-collection! — bash.d, Aug 20 '13 at 08:23
you can use the extension method Concat to concatenate two ienumerable — Fabio Marcolini, Aug 20 '13 at 08:23

score 14 · Answer 1 · answered Aug 20 '13 at 08:23

14

Could you not use Concat?

Something like

        IEnumerable<string> s1 = new List<string>
                                    {
                                        "tada"
                                    };
        IEnumerable<string> s2 = new List<string>
                                    {
                                        "Foo"
                                    };
        s1 = s1.Concat(s2);

answered Aug 20 '13 at 08:23

Adriaan Stander

162,879
31
289
284

+1 Concat is fine, also OP probably wants to concat multiple similar to King King SelectMany (+1 too) answer. – Alexei Levenkov Aug 20 '13 at 08:25
2

I think this is a misreading of the question. – Jodrell Aug 20 '13 at 08:33

King King · Answer 2 · 2013-08-20T08:43:44.037

3

var result = selected.Select(item=>_repo.GetAllDCategories(item))
                     .SelectMany(x=>x,(x,cat)=> select new {
                                                   label = cat.Name, 
                                                   value = cat.Id
                                                });

edited Aug 20 '13 at 08:43

answered Aug 20 '13 at 08:24

King King

61,710
16
105
130

Gave an error `The type arguments for method 'IEnumerable System.Linq.Enumerable.SelectMany (this IEnumerable, Func>)' cannot be inferred from the usage. Try specifying the type arguments explicitly.` I've put the type explicitly but didn't work! – SVI Aug 20 '13 at 08:36

Jodrell · Accepted Answer · 2013-08-20T08:46:27.700

Well, I think there is some confusion here,

var result = selected.SelectMany(item => 
    _repo.GetAllDCategories(item).Select(cat =>
        new
        {
            Label = cat.Name,
            Value = cat.Id
        });

seems to me what you want.

You can use SelectMany to "squash" or "flatten" an IEnumerable<IEnumerable<T>> into an IEnumerable<T>.

Its similar to having a function like this

IEnumerable<KeyValuePair<string, int>> GetSelectedCategories(
        IEnumerable<string> selected)
{
    foreach (var item in selected)
    {
        foreach (var category in _repo.GetAllDCategories(item))
        {
            yield return new KeyValuePair<string, int>(
                category.Name,
                category.Id);
        }
    }
}

Thanks! That's what I call a genius way to read & answer a question. Perfect! — SVI, Aug 20 '13 at 08:43

Adding IEnumerable items to IEnumerable

3 Answers3