Here is a peace of code:

void MyFunc(List<MyObj> objects)
{
  MyFunc1(objects);

  foreach( MyObj obj in objects.Where(obj1=>obj1.Good))
  {
    // Do Action With Good Object
  }
}

void MyFunc1(List<MyObj> objects)
{
  int iGoodCount = objects.Where(obj1=>obj1.Good).Count();
  BeHappy(iGoodCount);

  // do other stuff with 'objects' collection
}

Here we see that collection is analyzed twice and each time the value of 'Good' property is checked for each member: 1st time when calculating count of good objects, 2nd - when iterating through all good objects.

It is desirable to have that optimized, and here is a straightforward solution:

• before call to MyFunc1 makecreate an additional temporary collection of good objects only (goodObjects, it can be IEnumerable);
• get count of these objects and pass it as an additional parameter to MyFunc1;
• in the 'MyFunc' method iterate not through 'objects.Where(...)' but through the 'goodObjects' collection.

Not too bad approach (as far as I see), but additional parameter is required to be passed.

Question: is there any LinQ out-of-the-box functionality that allows any caching during 1st Where().Count(), remembering a processed collection and use it in the next iteration?

Any thoughts are welcome.

Thanks.