Decrement two numeric substrings in a year span expression

Question

I am trying to minus or subtract by 1 the academic year of school year with this format, e.g. "2020-2021"

If it is 2020-2021, I would like to change it 2019-2020. Is there a way to solve this concern?

I considered trying to subtract using a hyphenated expression, but I am pretty stuck.

echo "2020-2021"-"1-1";
echo "Result: 2019-2020";

[Split](https://www.php.net/manual/en/function.explode.php), [parse](https://www.php.net/manual/en/function.intval.php), subtract each then just recombine them. — Martheen, Nov 28 '22 at 05:59

score 1 · Answer 1 · answered Nov 28 '22 at 06:45

You can use explode and parse the value to subtract the value

    $minusYear = 1;
    $myString = "2020-2021";
    $myArray = explode('-', $myString);
  
  
    foreach($myArray as $k => $v)
    {
      $myArray[$k] = (int) $myArray[$k] - $minusYear;
    }
  
    echo "Result ".$myArray[0]."-".$myArray[1];

score 1 · Answer 2 · answered Nov 28 '22 at 06:58

You don't need to complicate your task by trying to shoehorn 1-1 into your approach. Use preg_replace_callback() to target and decrement numeric substrings in one line of code.

This approach targets the numbers and therefore will not break if your delimiting character(s) change.

Code: (Demo)

$yearSpan = '2020-2021';

echo preg_replace_callback('/\d+/', fn($m) => --$m[0], $yearSpan);

Decrementing the fullstring match --$m[0] could also be written as simple subtraction: $m[0] - 1.

Decrement two numeric substrings in a year span expression

2 Answers2