I have two Enumberable lists: list1 & list2 I want to take something from list2 and update it in list1 based on a condition

e.g: list1.Id has say for instance 1, 2, 3, 4, 5 etc. list2.Id has 3, 4 I need to compare these Ids and take the other fields(e.g. name, subject) from list2 which matches list1.Id (3 and 4 in this case) and copy it to list1 other fields(name, subject)

list1:

list2:

Required resultant:

CodePudding user response：

Lets say you have a class subject as below:

 class Suabject
    {
        public int id;
        public string name;
        public string Subject;
    }

and you have two lists as below:

    List<Suabject> enum1 = new List<Suabject>();
    List<Suabject> enum2 = new List<Suabject>();

If you want to merge them, what you do is basically go through all the items in enum2 and check if the item exist in the enum1 then u update it. If not, you can add it to the list. As below:

  foreach (var item in enum2)
            {
                var s = enum1.FirstOrDefault(x=> x.id == item.id);
                if(s != null)
                {
                    s.name = item.name;
                    s.Subject = item.Subject;
                }
                else
                    enum1.Add(s);
            }

In this way, enum1 will be the merged list of the two.

CodePudding user response：

How about this?

var listOne = new[]
{
    new Entity { Id = 1, Name = "N1", Subject = "S1" },
    new Entity { Id = 2, Name = "N2", Subject = "S2" },
    new Entity { Id = 3 },
    new Entity { Id = 4 },
    new Entity { Id = 5, Name = "N5", Subject = "S5" },
};

var listTwo = new[]
{
    new Entity { Id = 3, Name = "N3", Subject = "S3" },
    new Entity { Id = 4, Name = "N4", Subject = "S4" },
};

// Join to lists by using 1:1 relationship
var pairs = listOne.Join(listTwo, entity => entity.Id, entity => entity.Id, (one, two) => (one, two));

foreach (var pair in pairs)
{
    // Update first name, if empty
    if(string.IsNullOrEmpty(pair.one.Name))
        pair.one.Name = pair.two.Name;

    // Update first subject, if empty
    if(string.IsNullOrEmpty(pair.one.Subject))
        pair.one.Subject = pair.two.Subject;
}

// Save and show elements
foreach (var item in listOne)
{
    Console.WriteLine(JsonConvert.SerializeObject(item));
}

CodePudding user response：

If you are looking for a solution without a Foreach, have you thought of using Dictionaries for this part, where you set the key as the id of your object and the value as the object itself.

Dictionary<int, ObjectType> dictA = new Dictionary<int, ObjectType>();

where you add you values like this:

dictA.Add(object.Id, object);

Then you will be able to do a merge without a Foreach like this:

dictA = dictA.Concat(dictB.Where(b => !dictA.ContainsKey(b.Key))).ToDictionary(b => b.Key, b => b.Value);

This way, the dictB gets merged in the dictA. Just reverse the values if you want the opposite to happen.

CodePudding user response：

Not quite sure what do you need. I assume you need to update data in enum1 based on enum2, in that case do this:

foreach(var item in enum2)
{
    var itemToUpdate = enum1.SingleOrDefault(x => x.Id == item.Id);
    if (itemToUpdate == null) continue;
    itemToUpdate.Name = item.Name;
    itemToUpdate.Subject = item.Subject;
}