I have two list. ListA and ListB.

ListA

ID  Name    Age
001 Andy    null
002 Sam     null

ListB

ID  Name    Age
001 Andy    10

What I want to do is replace ListA's Age with ListB'Age based on two conditions using Linq. They are

ListA.ID == ListB.ID 
ListA.Name == ListB.Name

So, the final result would be:

ID  Name    Age
001 Andy    10
002 Sam     null

Please ignore column names because they are only for demo purpose.

CodePudding user response：

You can work with Linq, the concept is listA LEFT JOIN listB.

var result = (from a in listA
            join b in listB on new { a.ID, a.Name } equals new { b.ID, b.Name } into ab
            from b in ab.DefaultIfEmpty()
            select new People
            {
                ID = a.ID,
                Name = a.Name,
                Age = b?.Age
            }
        ).ToList();

Sample .NET Fiddle

CodePudding user response：

Given two list of items

List<ListItem> listA = new List<ListItem>();
List<ListItem> listB = new List<ListItem>();

of this type

    public class ListItem 
    {
        public string ID { get; set; }
        public string Name { get; set; }

        public int? Age { get; set; }
    }

you can change all listA Age values this way:

listA.ForEach(item => 
    item.Age = listB.Where(itemB => itemB.ID == item.ID && itemB.Name == item.Name)
    .FirstOrDefault()?.Age);

CodePudding user response：

using foreach and linq

public class emp
{
    public string ID { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

static void Main(string[] args)
{

    var ListA = new List<emp>();
    var ListB = new List<emp>();

    ListA.Add(new emp { ID = "001", Name = "Andy" });
    ListA.Add(new emp { ID = "002", Name = "Sam" });

    ListB.Add(new emp { ID = "001", Name = "Andy", Age = 10 });

    foreach (var emp in ListA)
    {
        var empfound = ListB.FirstOrDefault(lista => lista.ID == emp.ID);
        if (empfound != null) emp.Age = empfound.Age;
    }
}