Linq to update a collection with values from another collection?

Question

I have IQueryable baseList

and List someData

What I want to do is update attributes in some

Answer 1

As mentioned before, it should be a combination of loop and LINQ

foreach (var someDataItem in someData)
{
    someDataItem.PropertyToUpdate = (baseList.FirstOrDefault(baseListItem => baseListItem .key == someDataItem.key) ?? new SomeClass(){OtherProperty = "OptionalDefaultValue"}).OtherProperty;
}