更改日期数组的日期格式

Question

All documentation I find is on changing the date format of a string. How do I change the date format of a series of dates within an array? In my particular example I was hoping to show just the Year.

The following errors out since $years is an array.

$years = date_format($years, 'Y');

UPDATE

I was trying to submit this array as labels in a chart.js chart therefore I needed to add the & symbol within my foreach loop in order to have the original array reference updated as opposed to making a copy for it to work within chart.js.

foreach ($years as &$year)
    {
       $year = substr($year, 0, 4);
    }

Answer 1

If you're absolutely sure that the date's format will never change and you just need year ,you would be better off with this code.

$years=array('2016-20-02','2012-20-02','2013-20-02','2014-20-02','2011-20-02');
foreach($years as $yr)
{
    echo substr($yr, 0, 4)."<br>";
}