Programmatically Open Bootstrap UI Accordion Generated by Nested Ng-Repeat when Filtered Array is Not Empty

I have a Bootstrap-UI accordion group that generates individual accordion menus using ng-repeat. The content under each accordion is also generated using a nested ng-repeat.

<accordion close-others="false">
        <span data-ng-repeat="category in categories">
            <accordion-group is-open="filterText.length > 0">
                <accordion-heading>{{category}}: {{reportList.length}} Items </accordion-heading>
                <div>
                    <ul>
                        <li data-ng-repeat="report in reportList = (getReports($parent.$index) | filter: filterText)">{{report}}</li>
                    </ul>
                </div>
            </accordion-group>
        </span>
    </accordion>

The content generated by the second ng-repeat needs to be searchable. When the search is executed, accordions that contain matching values should open and display the matching values. I know that the outside ng-repeat sees the filtered array and its length because i can display the length value in the view (i.e. {{reportList.length}} updates when the filter executes).

The problem comes when i try to put the reportList.length value in the is-open attribute of an <accordion-group>. Using is-open="reportList.length" seems to pass the literal into the directive. In desperation, I tried using is-open="{{reportList.length}}" but that throws the expected syntax error.

Here's a plunker that shows what i have working as well commented out lines that show the way i think it should work (lines 22 & 23). Any suggestions are more than welcome.