How to Group Subarrays and Format Values by Column in PHP?

Group Subarrays by Column, Format Values from Other Column Within Groups

In a given array where each subarray consists of two columns, the task is to group the subarrays by the second column and create a new array where each group has the values from the first column concatenated with commas and the second column as the second value.

For example, an input array like:

$array = [
    ["444", "0081"],
    ["449", "0081"],
    ["451", "0081"],
    ["455", "2100"],
    ["469", "2100"]
];

should be transformed into:

array (
  0 => 
  array (
    0 => '444,449,451',
    1 => '0081',
  ),
  1 => 
  array (
    0 => '455,469',
    1 => '2100',
  ),
)

Solution:

A straightforward approach to achieve this is as follows:

<code class="php">// Create an empty array to store the grouped data
$groups = [];

// Loop through the input array
foreach ($array as $item) {
    // If the second column value is not yet a key in $groups, create an empty array for it
    if (!array_key_exists($item[1], $groups)) {
        $groups[$item[1]] = [];
    }
    
    // Add the first column value to the array at the corresponding key
    $groups[$item[1]][] = $item[0];
}

// Initialize the new array with the desired structure
$structured = [];

// Loop through the groups
foreach ($groups as $group => $values) {
    // Join the first column values with commas and add the group key as the second column
    $structured[] = [implode(',', $values), $group];
}</code>

This solution handles the transformation efficiently, resulting in the desired output.

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