Home ยป What is the least amount of code needed to update one list with another list?

What is the least amount of code needed to update one list with another list?

Solutons:


originalList = newList;

Or if you prefer them being distinct lists:

originalList = new List<int>(newList);

But, either way does what you want. By your rules, after updating, originalList will be identical to newList.

UPDATE: I thank you all for the support of this answer, but after a closer reading of the question, I believe my other response (below) is the correct one.

If you use some LINQ extension methods, you can do it in two lines:

originalList.RemoveAll(x => !newList.Contains(x));
originalList.AddRange(newList.Where(x => !originalList.Contains(x)));

This assumes (as do other people’s solutions) that you’ve overridden Equals in your original object. But if you can’t override Equals for some reason, you can create an IEqualityOperator like this:

class EqualThingTester : IEqualityComparer<Thing>
{
    public bool Equals(Thing x, Thing y)
    {
        return x.ParentID.Equals(y.ParentID);
    }

    public int GetHashCode(Thing obj)
    {
        return obj.ParentID.GetHashCode();
    }
}

Then the above lines become:

originalList.RemoveAll(x => !newList.Contains(x, new EqualThingTester()));
originalList.AddRange(newList.Where(x => !originalList.Contains(x, new EqualThingTester())));

And if you’re passing in an IEqualityOperator anyway, you can make the second line even shorter:

originalList.RemoveAll(x => !newList.Contains(x, new EqualThingTester()));
originalList.AddRange(newList.Except(originalList, new EqualThingTester()));

Sorry, wrote my first response before I saw your last paragraph.

for(int i = originalList.length-1; i >=0; --i)
{
     if (!newList.Contains(originalList[i])
            originalList.RemoveAt(i);
}

foreach(int n in newList)
{
     if (!originaList.Contains(n))
           originalList.Add(n);
}

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