angularjs nested ng-repeat child length outside ng-repeat

I have a nested ng-repeat, and am trying to use the length of the filtered nested ng-repeat outside the parent ng-repeat. However, the result is always 0 ,if it is a single ng-repeat I can get the result. I have tried $parent.filtered but it is getting wrong results.

example below:

 <div>
            Filtered Count :{{filtered.length}}
            <div ng-repeat="group in groups">
                <div ng-repeat="letter in  filtered = (group.letters | filter:filters.search )  | orderBy:orderByAttribute:sortReverse ">

                </div>
            </div>

        </div>

Thx,