Filter ng-options from ng-options selection

I'm hoping to solve three problems...

In my app page I have one select for states and another for counties. For states I have:

<select ng-model="filter.stateID" ng-options="item.stateID as item.state for item in st_option">
</select>

Data:

[
  { state="California", stateID="5"},
  { state="Arizona", stateID="3"},
  { state="Oregon", stateID="38"},
  { state="Texas", stateID="44"},
  { state="Utah", stateID="45"},
  { state="Nevada", stateID="29"}
]

For my County select I have:

<select ng-model="filter.countyID" ng-options="item.countyID as item.county for item in co_option">
 </select>

Data:

[
  { county="Orange", countyID="191", co_state_id="5"},
  { county="Multiple Counties", countyID="3178", co_state_id="3"},
  { county="Sonoma", countyID="218", co_state_id="38"},
  { county="Los Angeles", countyID="190", co_state_id="44"}
]

This is my ng-repeat:

<div ng-repeat="project in projects | filter:filter">
    <div>
        State: {{project.state}}<br> 
        County: {{project.county}}<br>
        <span ng-hide="{{project.stateID}}"></span>
        <span ng-hide="{{project.countyID}}"></span>
    </div>
</div>

So, as you can see I'm using the stateID on the state select and on the county select I have the corresponding state id set in co_state_id in the county data set.

I'd like to do a few things:

Hide the county select until a state is selected.
After a state is selected, filter the county select options by the selected stateID / co_state_id
Filter the ng-repeat by first the stateID, then by the countyID.

I also haven't see a way to set filter.stateID to true or filter by a number instead of a string. when I filter by stateID I get mixed results because some stateID's can have "1" in them..

Usually you only want to ask one question per post but i'll give these three a shot.

Part 1: Add an ng-show for filter.stateID. Since you can't deselect a state, you can use a one time binding if your angular is ^1.3.

<select ng-show="::filter.stateID" ng-model="filter.countyID" ng-options="item.countyID as item.county for item in co_option">

Part 2: Add filter for {co_state_id : filter.stateID}

<select ng-show="::filter.stateID != null" ng-model="filter.countyID" ng-options="item.countyID as item.county for item in co_option | filter:{ co_state_id : filter.stateID }">

Part 3:

You are using the pattern object for the filter, shouldn't matter if the value of the id is 1:

Object: A pattern object can be used to filter specific properties on objects contained by array. For example {name:"M", phone:"1"} predicate will return an array of items which have property name containing "M" and property phone containing "1". A special property name $ can be used (as in {$:"text"}) to accept a match against any property of the object or its nested object properties. That's equivalent to the simple substring match with a string as described above. The predicate can be negated by prefixing the string with !. For example {name: "!M"} predicate will return an array of items which have property name not containing "M".

Working Snippet

var app = angular.module('app', []);

app.controller('myController', function($scope) {
  $scope.projects = [{
    name: 'Project1',
    state: 'CA',
    stateID: '5',
    county: 'Orange',
    countyID: '191'
  }, {
    name: 'Project2',
    state: 'CA',
    stateID: '5',
    county: 'LosAngeles',
    countyID: '190'
  }, {
    name: 'Project3',
    state: 'CA',
    stateID: '5',
    county: 'Orange',
    countyID: '191'
  }, {
    name: 'Project4',
    state: 'MadeUp',
    stateID: '1',
    county: 'MadeUp',
    countyID: '190'
  }];

  $scope.st_option = [{
    state: "California",
    stateID: "5"
  }, {
    state: "Arizona",
    stateID: "3"
  }, {
    state: "Oregon",
    stateID: "38"
  }, {
    state: "Texas",
    stateID: "44"
  }, {
    state: "Utah",
    stateID: "45"
  }, {
    state: "Nevada",
    stateID: "29"
  }];

  $scope.co_option = [{
    county: "Orange",
    countyID: "191",
    co_state_id: "5"
  }, {
    county: "Multiple Counties",
    countyID: "3178",
    co_state_id: "3"
  }, {
    county: "Sonoma",
    countyID: "218",
    co_state_id: "38"
  }, {
    county: "Los Angeles",
    countyID: "190",
    co_state_id: "44"
  }];

  $scope.filter = {};
});

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.15/angular.min.js"></script>
<div ng-app='app' ng-controller='myController'>
  <select ng-model="filter.stateID" 
          ng-options="item.stateID as item.state for item in st_option"></select>
  <select ng-show="::filter.stateID" 
          ng-model="filter.countyID" 
          ng-options="item.countyID as item.county for item in co_option | filter:{ co_state_id : filter.stateID }">
  </select>

  <div ng-repeat="project in projects | filter:filter">
    <div>
      <br>Name: {{ project.name }}
      <br>State: {{project.state}}
      <br>County: {{project.county}}
      <br>
      <span ng-hide="{{project.stateID}} "></span>
      <span ng-hide="{{project.countyID}} "></span>
    </div>
  </div>
</div>