Filter city based on state in JSON in php

i am using city and state list json from below link,

https://github.com/nshntarora/Indian-Cities-JSON/blob/master/cities.json

Format is like below,

[
    {
        "id": "1",
        "name": "Mumbai",
        "state": "Maharashtra"
    },
    {
        "id": "2",
        "name": "Delhi",
        "state": "Delhi"
    },
    {
        "id": "3",
        "name": "Bengaluru",
        "state": "Karnataka"
    },
	{
        "id": "4",
        "name": "Mysore",
        "state": "Karnataka"
    },
]

Here state is repeating for different cities now i want to display all states in select box for that i want to fetch state value which are unique and display in select box. then on change of state i want to fetch all data which matches state name.

i am storing this json in .json file and fetching the data like below,

$getjson = file_get_contents("./assets/statescities.json");
$statesresult = json_decode($getjson, true);

Any help? Thank you