C# searching through lists

Question

Hi,

In the following code I'm using 3 foreach statements. I'm just looking to populate a list when a list of items matches another but the ones that don't match also have to be added. So I was wondering if there is an easier way to do the following.

        List<T> ds = new List<T>();  //is populated           
        foreach (var b in template.Bs)
        {
            List<BD> tempList = new List<BD>();
            foreach (BD bd in b.BDs)
            {
                Boolean found = false;
                foreach (DV dv in items)
                {
                    if (bd.C == dv.C)
                    {
                        found = true;
                        tempList.Add(new BD ()
                        {
                            //populating
                        });
                    }
                }
                if (!found)
                    tempList.Add(new BD()
                    {
                        //populating
                    });
            }

        }

Answer 1

The relationship between ds and tempList is not clear, but it looks to me like your inner loops are really a left outer join:

List<T> ds = new List<T>();  //is populated           
foreach (var b in template.Bs)
{
    var newBDs = from bd in b.BDs
                 join dv in items on bd.C equals dv.C into j
                 from dv in j.DefaultIfEmpty()
                 select dv == null ? NoMatch(bd) : Match(bd, dv);

    List<BD> tempList = newBDs.ToList();

    // Do something with tempList
}

For each b in template.Bs, we're matching bd's from b.BDs with dv's in items. We then use DefaultIfEmpty() to put null in dv if there was no match, which we then use to determine which projection method to call: NoMatch() would create a new BD based on the unmatched bd, and Match() would create a new BD based on the matched bd and dv.

That whole query is represented by newBDs, which will be IEnumerable<BD>. We can then buffer that sequence into tempList or do something else useful with it.