在ui select中禁用重复列表中的一个或多个项目

$scope.list = ['item1', 'item2', 'item3', 'item4']

<ui-select ng-model="item"
           on-select="changeItem()"
           ng-disabled="isReadOnly()" required>

    <ui-select-match class="ui-select-match">
        <span ng-bind="$select.selected"></span>
    </ui-select-match>
    <ui-select-choices class="ui-select-choices"
                       repeat="item in list">
        <div class="row">
            <div class="col-md-12">
                <span ng-bind="item"></span>
            </div>
        </div>
    </ui-select-choices>
</ui-select>