Form date from foreach loop through object - php

Question

So I have an array of objects that looks like this:
credit_cards[[0] => {expiration_date: {year: "17", month: "04"}]
What I try to do is somethings like this:
$years = [];
$months = [];
$dates = [];
foreach ($clients->settings->credit_cards as $key => $value){
$years[] = $value->expiration_date->year;
$months[] = $value->expiration_date->month;
}
I need to loop through every credit card in that array and make an array $dates that should form a basic date by concatenating years and months. So in this case it should look like this: $dates = ['2017-04']. But I have no idea how to do this. Any help is welcomed and some explanation if you may so I can understand how to do this in the future.

Answer 1

You can just add the dates with a minor amount of work. create a parseable string that represents your Month / Year. Then put it in php's strtotime(). That integer representing seconds since the epoch is the 2nd argument to format the four digit date -dash- month that you are looking for.
$years[] = $value->expiration_date->year;
$months[] = $value->expiration_date->month);
$my = $value->expiration_date->month.'/'.$value->expiration_date->year;
$dates[] = date('Y-m', strtotime($my));

Answer 2

You're looking for the concatenate operator: . (More info here.) You can build a formatted date string and pass it to strtotime like WEBjuju's answer, or move directly to using the concatenation.
$years[] = $value->expiration_date->year;
$months[] = $value->expiration_date->month;
$dates[] = $value->expiration_date->year . '-' . $value->expiration_date->month;