$scope$watch change one var if another changed - angularjs

Question

so i have to scope objects
$scope.hf_directory = data.features;
$scope.brylanty = data.features;
Actually they contain the same data, but i am trying to know how watch works so then i can use it in my project.
And i would like to watch hf_directory on which i use filter:search, so it would update scope.brylanty after typing something in input fiels ng-model="search"
i tried to do something like this but not making any changes
$scope.$watch('hf_directory', function (newValue, oldValue, $scope) {
if(newValue) {
$scope.brylanty = newValue;
}
});
Both scope objects are displayed by ng-repeat loop, on first i use filter:search on another nothing, i know i could just use another filter:search, but i want to learn how to use watch ;)
My objects are geojson data, they containt the same value, geojson look like below:
{
"type": "FeatureCollection",
"crs": { "type": "name", "properties": { "name": "urn:ogc:def:crs:OGC:1.3:CRS84" } },
"features": [
{ "type": "Feature", "properties": { "name": "SomeName"}, "geometry": { "type": "Point", "coordinates": [ 11.410585, 11.293361 ] } },
{ "type": "Feature", "properties": { "name": , "SecondName": { "type": "Point", "coordinates": [ 11.410585, 11.293361 ] } }, .......
]
}
After Your advices guys i tried this
$scope.search = {};
$scope.$watch('search', function (newVal) {
$scope.brylanty = newVal;
});
And this
$scope.$watch('search', function (newValue, oldValue, $scope) {
if (newValue) {
$scope.brylanty = newValue;
}
});
But without any good results, in both cases when i start typing something object brylanty is disappearing?

Answer 1

If you want to make changes upon typing something in the input ng-model="search" then ideally you should be watching the search variable. It should be
$scope.$watch('search', function (newValue, oldValue, $scope) {
if(newValue) {
$scope.brylanty = newValue;
}
});
This can also be written as (for 2 lines less)
$scope.$watch('search', function (newValue, oldValue, $scope) {
$scope.brylanty = (newValue) ? newValue : $scope.brylanty;
});
alternatively you could use ng-change in your input field and have
<input ng-model="search" ng-change="brylanty = (search) ? search : brylanty"/>
Watching hf_directory has no effect since typing in search doesn't affect it.
Edit: if you really want to watch hf_directory and it's an object/array then use
$scope.$watchCollection()
with the same arguments

Answer 2

UPDATE Added Demo
According to Docs
You can watch any variable by doing something like
$scope.$watch(function(){
return $scope.hf_directory; // or Directories.hf_directory if Directory is a factory/service
}, function(newVal, oldVal){
if(newVal != oldVal){
$scope.newestValue = newVal; // Do some cool UI
}
}, true); // true to check object equality (see below)
object equality is equivalent to angular.equal Source
I hope this helps.