How to use a variable with ng-if in AngularJS

I'm new to angularJS / Jade / HTML. I want to filter my displayed element by department.id with ng-if but I don't undestand how to get the filter they select in input. They have to choose a department Label, and i want to stock the id of this department without passing by a controller.

Here is the code to display the element :

  .col-md-3(ng-repeat="user in refs.userList | orderBy : 'department.id'", ng-if="user.department.id == 5")

I want to change the "== 5" with a variable stocked before.

I've tried something like this but I'm not sure :

sk-input-select(ng-model=#THE VARIABLE#, choices="refs.departmentList", placeholder='Sélectionner...', allow-clear='true')

Thanks,

Nicolas