How to sort an array of dates and times?

PHP: How to sort an array of dates and times?

Table of contents

  1. First, convert the dates into a timestamp

    In PHP it is very easy to sort an array of dates and times. All you need to do is convert it to a (integer) timestamp, and then do a normal sort. Here are more details:

    First, convert the dates into a timestamp

    A timestamp is time measured in the number of seconds since the Unix Epoch (January 1 1970 00:00:00 GMT). The current timestamp (when this page was last cached, anyway) is: 1550289609 (time()).

    Because there is no standard PHP array function for sorting date strings we will have to convert it ourselves. But we can make a closure, and pass that to usort(&$array, $compare_func) (which lets us define our own function to do the comparisons for the sorting)

    The custom comparison function for usort takes 2 parameters. It returns either -1, 0, or 1 depending on how they compare (1 if $a is less than $b; -1 if $a is greater than $b; 0 if equal). We can use PHP's spaceship operator for this (<=>) .

    Let's set up the data:

    1.     $dates = [
    2.  
    3.     "10 September 2000",
    4.     "10 September 2020",
    5.     "9 September 2020",
    6.     "9 September 2000",
    7.     "5 April 1999",
    8.     "20 April 1998",
    9. ];

    And now the comparison function:

    1. $compare_function = function($a,$b) {
    2.  
    3.         $a_timestamp = strtotime($a); // convert a (string) date/time to a (int) timestamp
    4.         $b_timestamp = strtotime($b);
    5.  
    6.         // new feature in php 7
    7.         return $a_timestamp <=> $b_timestamp;
    8.  
    9.         /* old way to do it:
    10.  
    11.                 if ($a_timestamp > $b_timestamp) {
    12.                     return -1;
    13.                 }
    14.                 elseif ($a_timestamp < $b_timestamp) {
    15.                     return 1;
    16.                 }
    17.                 else {
    18.                     return 0;
    19.                 }
    20.  
    21.         */
    22.  
    23.                 };

    Now we have everything we need - let's sort that data!

    1.         usort($dates, $compare_function);
    2.         var_dump($dates);
    array:6 [
  0 => "20 April 1998"
  1 => "5 April 1999"
  2 => "9 September 2000"
  3 => "10 September 2000"
  4 => "9 September 2020"
  5 => "10 September 2020"
]
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    webdevetc

    I am a 29 year old backend web developer from London, mostly focusing on PHP and Laravel lately. This (webdevetc.com) is my blog where I write about some web development topics (PHP, Laravel, Javascript, and some server stuff). contact me here.



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