Nested Lambda expression instead of foreach

Question

class A{
    public B body { get; set; }
}

class B{
    public List<C> positions { get; set; }
}

class C{
    public string NameOfWeek { get; set; }
}

class week{
    public int ID { get; set; }
    public string NameOfWeek { get; set; }
}

class SomeX{
    public List<A> MapWeekID(List<week> weekList, List<A> AList)
        {
            foreach (var a in AList)
            {
                foreach (var position in a.body.positions)
                {
                    position.NameOfWeek = weekList
                        .Where(x => x.NameOfWeek.ToString() == position.NameOfWeek)
                        .Select(y => y.NameOfWeek)
                        .FirstOrDefault();
                }
            }

            return AList;
        }
}

Here is code. How to write lambda for above foreach statement? I am trying but couldn't get hold of best solution so can anyone?

Linq is not very good when you want to modify an existing collection (AList). I suggest keeping foreach — Dmitrii Bychenko
– Dmitrii Bychenko, Commented Sep 5, 2018 at 22:15

Gauravsa · Accepted Answer · 2018-09-06 00:21:38Z

1

Well, you can use the linq function SelectMany. Here is a modified version:

foreach(var position in AList.SelectMany(k => k.body.positions)) {
    position.NameOfWeek = weekList
                        .Where(x => x.NameOfWeek.ToString() == position.NameOfWeek)
                        .Select(y => y.NameOfWeek)
                        .FirstOrDefault();
}

answered Sep 6, 2018 at 0:21

Gauravsa

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Comments

halfer · Accepted Answer · 2022-06-19 09:11:39Z

1

Linq and Extension Methods shouldn't really try to solve everything. However, if you really need everything in the one statement, you could use this.

AList.SelectMany(x => x.body.positions)
     .ToList()
     .ForEach(
         position => 
            position.NameOfWeek = weekList.Where(x => x.NameOfWeek == position.NameOfWeek)
                                          .Select(y => y.NameOfWeek)
                                          .FirstOrDefault());

Note : If this came across my desk for code review, I'd send it back with a note asking for a refactor.

Basically, your original foreach is easy to read and maintain. It's not trying to be too fancy, and you can easily see what's going on. These qualities are way more important then getting everything in one statement.

edited Jun 19, 2022 at 9:11

halfer

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answered Sep 5, 2018 at 23:26

TheGeneral

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1 Comment

rANth Over a year ago

Thank you for your positive comment :)

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