How to Group Rows in a 2D Array by One Column and Sum Another?

Reducing a 2D Array by Grouping Rows by One Column and Summing Another within Each Group

In this scenario, you seek to manipulate a 2D array by organizing its rows based on a specific column while aggregating the values of another column within each group created.

To address this need, consider employing an iterative approach through the rows of the input array:

$in = array(
    ['quantity' => 5, 'dd' => '01-Nov-2012'],
    ['quantity' => 10, 'dd' => '01-Nov-2012'],
    ['quantity' => 3, 'dd' => '02-Nov-2012'],
    ['quantity' => 4, 'dd' => '03-Nov-2012'],
    ['quantity' => 15, 'dd' => '03-Nov-2012'],
);

Create an empty output array:

$out = array();

Now, traverse each row:

foreach ($in as $row) {

Within each row, check if the dd value is already present in the $out array:

if (!isset($out[$row['dd']])) {

If not, create a new entry for the dd value with initialized 'quantity':

$out[$row['dd']] = array(
    'dd' => $row['dd'],
    'quantity' => 0,
);

Regardless, update the quantity value by adding the current row's quantity:

$out[$row['dd']]['quantity'] += $row['quantity'];

Finally, numerically index the $out array to achieve the desired reduced 2D array:

$out = array_values($out);

As a result, you obtain the summarized array with grouped rows:

var_dump($out);

[
    ['quantity' => 15, 'dd' => '01-Nov-2012'],
    ['quantity' => 3, 'dd' => '02-Nov-2012'],
    ['quantity' => 19, 'dd' => '03-Nov-2012'],
]

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