'Updating fields in one list from another list [closed]

Is there a better or more efficient way to do this?

Both of these objects have the same Id and some similar fields that I want to update.

foreach (var i in oldItems)
{
   foreach (var j in newItemValues)
   {
       if(i.id == j.Id)
       {
           j.field1 = (decimal)i.field1;
           j.field2 = (decimal)i.field2;
       }
   }
}
c++sharp.net


Solution 1:[1]

try this maybe you are like this;

foreach (var n in newItemValues)
{
    Item item = oldItems.FirstOrDefault(x => x.Id == n.Id);

    if (item != null)
    {
        n.field1 = item.field1;
        n.field2 = item.field2;
    }
}

Edit: If you keep oldItems in a HashSet or HashTable by keeping key as Id the time taken will slow to O(N).

Solution 2:[2]

Convert oldItems or newItemValues into a Map before looping.

That will reduce computational complexity from O(n^2) to O(n)

Solution 3:[3]

You can do this by Linq Query

newItemsValues = 
            (from t1 in oldItems
             join t2 in newItemsValues on t1.Id equals t2.Id
             select new YourModel { field1 =  t1.field1 ,field2 = t1.field2 }
            ).ToList();

result will a list of all matching items where oldItems Id will be equals to newItemsValues Id

Sources

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Source: Stack Overflow

Solution Source
Solution 1
Solution 2 Sergey Alaev
Solution 3

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