How to convert the foreach loop to linq

Question

Code:

           foreach (var item in testItems.Distinct())
            {
                if (!testMap.ContainsKey(item.GetId()))
                {
                    testMap.Add(item.GetId(), item);
                }
            }

How to convert the foreach loop to linq for the above code? Thanks.

Answer 1

Sometimes the correct approach to "converting {x} to LINQ" is: don't. It isn't an appropriate tool for every job. Your current code with foreach and dictionary mutation is fine as it is. Keep it.

If duplicate ids (after the Distinct() ) aren't an issue, you could perhaps do:

var map = testItems.Distinct().ToDictionary(x => x.GetId());

But that's about it.

Answer 2

testItems.ToList().ForEach(item=>
{
 if (!testMap.ContainsKey(item.GetId()))
 {
   testMap.Add(item.GetId(), item);
 }
});

Answer 3

For a 1 line version, you could try this:

testItems.Distinct().Where(i => !testMap.ContainsKey(i.GetId()).ForEach(f => testMap.Add(f.GetId, f));

That will do the whole operation in one line, although I am not a big fan of doing everything at once as it can be harder to debug.