Group every three rows in a 2d array and sum one column

Question

I need to group 3 rows together, sum their salary values and access the month name from the next row (next calendar month).

$salaries =
[
    [
        'month'=>'January',
        'salary'=>200
    ],
    [
        'month'=>'Februray',
        'salary'=>300
    ],
    [
        'month'=>'March',
        'salary'=>400
    ],
    [
        'month'=>'April',
        'salary'=>500
    ],
    [
        'month'=>'May',
        'salary'=>600
    ],
    [
        'month'=>'June',
        'salary'=>700
    ],
    [
        'month'=>'July',
        'salary'=>800
    ],
    [
        'month'=>'August',
        'salary'=>900
    ],
    [
        'month'=>'September',
        'salary'=>1000
    ],
    [
        'month'=>'October',
        'salary'=>1100
    ],
    [
        'month'=>'November',
        'salary'=>130
    ],
    [
        'month'=>'December',
        'salary'=>1200
    ]
];

I tried the code on this page, but I don't know how to specify the 4th month with the sum.

If possible, I want this:

Array
(
    [0] => 
[
'month'=>'April'
'sum'=900
]
    [1] => 
[
'month'=>'other month'
'sum'=1800
]
    [2] => 
[
'month'=>'other month'
'sum'=2700
]
    [3] => 
[
'month'=>'other month'
'sum'=2430
]
)

I tried with this code:

$groupSum = []; 
foreach (array_chunk($salaries , 3) as $key => $value) { 
    $groupSum[] = array_reduce($value, function ($sum, $item) { 
        $sum += $item['salary']; return $sum; 
    }); 
}

And the result is :

Array ( 
    [0] => 900
    [1] => 1800
    [2] => 2700
    [3] => 2430
)

Answer 1

A (very) basic solution (for my tests, I fix the typo on February month name) :

function getNextMonth($month) {
    $months = ['January','February','March','April','May','June','July','August','September','October','November','December'];

    $pos = array_search($month, $months);

    if ($pos === false) {
        throw new Exception('Invalid month');
    }

    if ($pos == 11) {
        return 'January';
        // should return also year + 1
    }

    return $months[$pos+1];
}

$i = 1;
$trimestreSum = 0;
$trimestres = [];
foreach($salaries as $month) {
    $trimestreSum += $month['salary'];
    if ($i % 3 == 0) {
        array_push($trimestres, [
            'month' => getNextMonth($month['month']),
            'sum' => $trimestreSum,
        ]);
        $i = 0;
        $trimestreSum = 0;
    }
    $i++;

}

print_r($trimestres);

The result is

    Array
(
    [0] => Array
        (
            [month] => April
            [sum] => 900
        )
    [1] => Array
        (
            [month] => July
            [sum] => 1800
        )
    [2] => Array
        (
            [month] => October
            [sum] => 2700
        )
    [3] => Array
        (
            [month] => January
            [sum] => 2430
        )
)

The getNextMonth may be the only piece of code you need to add to your own code :)

Pretty sure that there are shorter (and more elegant) solutions, but hope that helps anyway.