Filters are a feature of AngularJS and not specific to Ionic. The main reason you might want to use a filter is when you just need the data to be displayed in a different format in the view. You don't want to change the actual value in the controller or factory. This makes things very convenient because you don't have to decide upon a specific format within the controller code while leaving the flexibility in the view component.
Here is the list of some out-of-the-box filters (from https://docs.angularjs.org/api/ng/filter):
In this recipe, you will learn how to add more filters using the
angular-filter module as well as create a custom filter. The following is the screenshot ...