根据另一个集合过滤一个集合

Question

I have a List<businessobject> object collection and a List<string> object collection. I want filter my List<businessobject> so that if a certain property in the business object equals anything the List<string> it will be filtered out. I can think of writing the code this way, but is there any faster or better way?

List<businessobject> bo = loadBusinessObjectList();
List<string> stringList = loadStringList();
foreach(businessobject busobj in bo){
   if(stringList.contains(busobj.myProperty))
      bo.remove(busobj)
}

Answer 1

Your original code will actually not work because you modify the List that you are enumerating.

You can do something like:

List<businessobject> bo = loadBusinessObjectList();
List<string> stringList = loadStringList();

var matches = (from b in bo where stringList.Contains(b.SomeProperty) select b);
var bo = bo.Intersect(matches);

If you modify

List<string> stringList

to be

HashSet<string> stringList

performance would be improved, particularly if the number of strings is large because testing for list membership is O(n), while testing for hashset membership approaches O(1).

Answer 2

Linq is your friend!

List<businessobject> boList = loadBusinessObjectList();
List<string> stringList = loadStringList();

var badObjects = from bo in boList
             where stringList.Contains(bo.myProperty)
             select bo;

boList.RemoveRange(badObjects); 

Answer 3

比到目前为止发布的其余代码简单得多...

bo.Where(o => !stringList.Contains(o.MyProperty));

Answer 4

List<businessobject> bo = loadBusinessObjectList();
List<string> stringList = loadStringList();
List<businesssobject> bo2 = bo.FindAll(obj => !(stringList.contains(obj.myProperty)));

Not sure if this is faster. Instead of removing the objects this one creates a new object with only the ones that match.