Count number of given object in a list with LINQ

问题

I have a list which can contain multiple occurrences of the same object. Now I need to count, how often the given object is contained in this list.

int count = 0;
foreach (IMyObject item in myList)
  if (item == object2Count)
    count++;

I am sure that this can be done nicer with LINQ, but LINQ is still a mystery to me.

My first question is: How would I count the objects via LINQ and the second question: Will this LINQ version be slower or faster? I am using a ObservableCollection and the number of items in the list is usally rather small ... usally not more then 20.

Thanks in advance,
Frank

回答1:

You can easily count objects in a collection using the Count extension method. Either:

var count = myList.Where(item => item == object2Count).Count();

or

var count = myList.Count(item => item == object2Count);

With regards to performance it should be the same as the foreach loop.

(Your predicate item == object2Count looks a bit weird but that is not related to the question about how to count objects in a collection.)

回答2:

int count = myList.Count(x => x == object2Count);

回答3:

Look at 101 LINQ Samples

int count = myList.Count(item => item == object2Count);

回答4:

Try this:

var count = objectlist.Count(x => x == object2Count));

来源：https://stackoverflow.com/questions/6408972/count-number-of-given-object-in-a-list-with-linq