如何仅从日期 arrays 中获取最小值和最大值？

Question

I have a date array containing only month and year..I want to get min and max date from this.

$dates = array('1-2018','5-2019','10-2018','5-2020');

Answer 1

You should transform all your string in DateTime object with DateTime::createFromFormat method

$dates = array_map(function($date){
  return DateTime::createFromFormat('m-Y',$date);
}, $dates);

Then sort them with sort function

sort($dates);

Answer 2

use usort. usort need a function for compare. A string with only month-year can not parse with strtotime. With a Day (i use simple the 1-) returns strtotime a correct timestamp. This funktion is for a ascendig sort. For descendig sort you must only switch $a and $b. I have add some values to the array for a better test.

<?php
$dates = array('1-2018','5-2019','10-2018','5-2020','9-1978','6-2001');

usort($dates, function($a,$b){ return strtotime('1-'.$a) <=> strtotime('1-'.$b);});

echo "<pre>".var_export($dates, true)."\n";

echo "Min: ".reset($dates)."\n";
echo "Max: ".end($dates)."\n";

Edit: The minimum is the first value from the array, the maximum is the last value.

Output:

array (
  0 => '9-1978',
  1 => '6-2001',
  2 => '1-2018',
  3 => '10-2018',
  4 => '5-2019',
  5 => '5-2020',
)
 Min: 9-1978
 Max: 5-2020

Demo: https://3v4l.org/lZocQ