Merge 2d array rows with same column value and sum another column [duplicate]

Use function array_reduce() to combine the items having the same city:

$input = array(
    array('city' => 'NewYork',      'cash' => '1000'),
    array('city' => 'Philadelphia', 'cash' => '2300'),
    array('city' => 'NewYork',      'cash' => '2000'),
);

$output = array_reduce(
    // Process the input list
    $input,
    // Add each $item from $input to $carry (partial results)
    function (array $carry, array $item) {
        $city = $item['city'];
        // Check if this city already exists in the partial results list
        if (array_key_exists($city, $carry)) {
            // Update the existing item
            $carry[$city]['cash'] += $item['cash'];
        } else {
            // Create a new item, index by city
            $carry[$city] = $item;
        }
        // Always return the updated partial result
        return $carry;
    },
    // Start with an empty list
    array()
);