PHP: How can I create a new array of data from another array by counting the occurrence of dates?

I need your help. I want to prepare some data from a multidimensional array of objects to equal with the ChartJS data structure:

https://www.chartjs.org/docs/master/general/data-structures/

So for example this array here:

$source = [
    [
        'id'           => '123',
        'date_created' => '2020-10-19 22:50:46'
    ],
    [
        'id'           => '456',
        'date_created' => '2020-10-19 13:50:19'
    ],
    [
        'id'           => '276',
        'date_created' => '2020-09-19 11:50:46'
    ],
    [
        'id'           => '846',
        'date_created' => '2020-09-19 21:50:46'
    ],
    [
        'id'           => '543',
        'date_created' => '2020-10-18 22:50:46'
    ]
];

needs to be transformed to:

$dest = [
    '2020-10-19' => '2',
    '2020-09-19' => '2',
    '2020-10-18' => '1'
];

So logically the functions needs to count the occurrence of timestamps in an array only by the date (not the time). After that a new array must be created with the date as key and the occurrences of it as a value.

I’ve tried using this:

error_log( print_r( array_count_values( array_flip( array_column( $source, 'date_exported' ) ) ), true ) );

But this only returns an array of the occurrences of the columns. So how can I deal with this the right way?

Answer

Try this.

<?php

// Your input array.
$source = [
    [
        'id'           => '123',
        'date_created' => '2020-10-19 22:50:46'
    ],
    [
        'id'           => '456',
        'date_created' => '2020-10-19 13:50:19'
    ],
    [
        'id'           => '276',
        'date_created' => '2020-09-19 11:50:46'
    ],
    [
        'id'           => '846',
        'date_created' => '2020-09-19 21:50:46'
    ],
    [
        'id'           => '543',
        'date_created' => '2020-10-18 22:50:46'
    ]
];

// Output array.
$output = [];

// Loop over each element and extract its key.
foreach ($source as $element)
{
    // Turn date string into DateTime object.
    $dateTime = new DateTime($element['date_created']);
    // Get the intended key in Y-m-d format.
    $key = $dateTime->format('Y-m-d'); 
    
    // New key? Initialize to 1.
    if (!isset($output[$key]))
        $output[$key] = 1;
    else
        // Existing key, increment.
        $output[$key]++;
}

var_dump($output);
/*
array(3) {
  ["2020-10-19"]=>
  int(2)
  ["2020-09-19"]=>
  int(2)
  ["2020-10-18"]=>
  int(1)
}
*/

OR

// Output array.
$output = [];

foreach ($source as $element)
{
    $key = explode(' ', $element['date_created'])[0];
    if (isset($output[$key]))
        $output[$key]++;
    else
        $output[$key] = 1;
}

var_dump($output);
/*
array(3) {
  ["2020-10-19"]=>
  int(2)
  ["2020-09-19"]=>
  int(2)
  ["2020-10-18"]=>
  int(1)
}
*/

OR, as a one liner:

// Output array.
$output = [];

var_dump(array_count_values(array_map(function ($element) { return explode(' ', $element)[0]; }, array_column($source, 'date_created'))));
/*
array(3) {
  ["2020-10-19"]=>
  int(2)
  ["2020-09-19"]=>
  int(2)
  ["2020-10-18"]=>
  int(1)
}
*/