How to Group a Multidimensional Array by a Particular Subarray Value

var arr = [["x","x", 1],["x","x", 2],["x","x", 2],["x","x", 3],["x","x", 3],["x","x", 3]], obj = {};


arr.forEach(v => (obj[v[2]] || (obj[v[2]] = [])).push(v));

var res = Object.keys(obj).map(v => obj[v]);


console.log(JSON.stringify(res));

How to group multidimensional array by sub-array value in and reassign keys in PHP

this should be enough, if I understood you right :)

$lines = file('./schedule.txt');

$employees = array();
foreach ($lines as $line)
{
    $chunks = explode(',', $line);
    $employees[$chunks[0]][] = array_slice($chunks, 1);
}

print_r($employees);

Group and merge subarray data based on one column value

A simple loop should do this..

$group = [];
foreach ($data as $item)  {
    if (!isset($group[$item['date']])) {
        $group[$item['date']] = [];
    }
    foreach ($item as $key => $value) {
        if ($key == 'date') continue;
        $group[$item['date']][$key] = $value;
    }
}

PHP multidimensional array: group repeated values and create sub array

Nothing wrong with the code you've provided at the end, but here's some ideas for how to make it more tolerant to more array values (as you mentioned, phone, email, etc).

This uses the handy PHP array_diff_key function to remove the array elements you don't want from the "core" records. Then, applying array_diff_key to get those same array elements INTO the "company" records.

// set up the array of keys you don't want in the "original" record
$exclude = ['company' => FALSE, 'price' => FALSE];
// Your original loop
foreach($array as $v) {
    // not strictly necessary, but helps readability
    $id = $v['id'];
    // Assign the "core" record all the values you want, excluding those defined above
    // in this case, will remove "company" and "price"
    $record = array_diff_key( $v, $exclude );

    // only set this if not already set, otherwise wipes out previous companies
    if ( ! isset($result[$id] ) ) {
        $result[$id] = $record;
        $result[$id]['companies'] = [];
    }

    // strip off the OTHER values from the array you don't want stored with the company
    // this will automatically pick up the field NOT excluded above
    // in this case, will remove all BUT "company" and "price"
    $company = array_diff_key( $v, $record );
    $result[$id]['companies'][] = $company;
}

Group array row on one column and form subarrays of varying depth/structure

UPDATE: Added a correction for the desired output at the bottom.

This seems easy, but is rather difficult to do right. The best approach is to divide and conquer. First collect the data together, which belongs together, and then make the nice JSON output. My first step is therefore this:

$input = [['color'=>'#000000','size'=>'L','count'=>2],
          ['color'=>'#000000','size'=>'XL','count'=>1],
          ['color'=>'#ffffff','size'=>'L','count'=>2],
          ['color'=>'#ffffff','size'=>'XL','count'=>1],
          ['color'=>'#ff0000','size'=>'L','count'=>1]];
          
$colors = [];

foreach ($input as $product) {
    extract($product);
    $colors[$color][$size] = $count;
}

echo json_encode($colors,  JSON_PRETTY_PRINT);

This outputs:

Array
(
    [#000000] => Array
        (
            [L] => 2
            [XL] => 1
        )

    [#ffffff] => Array
        (
            [L] => 2
            [XL] => 1
        )

    [#ff0000] => Array
        (
            [L] => 1
        )

)

Please note that extract() should be used with care, since it can generate more variables than you bargained for, but it is very useful here. Never use it at the global scope, like I did here.

And now we turn this into the wanted JSON, like this:

$output = [];

foreach ($colors as $color => $sizes) {
    $data = [];
    foreach ($sizes as $size => $count) {
        $data[] = ['value' => $size,
                   'count' => $count];
    }
    $output[] = ['color' => $color,
                 'size'  => $data];
}
          
echo json_encode($output,  JSON_PRETTY_PRINT);

This outputs:

[
    {
        "color": "#000000",
        "size": [
            {
                "value": "L",
                "count": 2
            },
            {
                "value": "XL",
                "count": 1
            }
        ]
    },
    {
        "color": "#ffffff",
        "size": [
            {
                "value": "L",
                "count": 2
            },
            {
                "value": "XL",
                "count": 1
            }
        ]
    },
    {
        "color": "#ff0000",
        "size": [
            {
                "value": "L",
                "count": 1
            }
        ]
    }
]

You might want to put all this code inside a function.

Here's a PHPFiddle.

NOTE: It is important to note that this code assumes that there are no duplicate color/size combinations in the input array.

In case the output you want wasn't a result of a typo, here's how you can modify the second loop to get it:

$output = [];

foreach ($colors as $color => $sizes) {
    $data = [];
    foreach ($sizes as $size => $count) {
        $data[] = ['value' => $size,
                   'count' => $count];
    }
    if (count($data) == 1) {
        $output[] = ['color' => $color,
                     'size'  => $data[0]['value'],
                     'count' => $data[0]['count']];
    } else {
        $output[] = ['color' => $color,
                     'size'  => $data];
    }                     
}
          
echo json_encode($output,  JSON_PRETTY_PRINT);

See this PHPFiddle

Group array by subarray values

$arr = array();

foreach ($old_arr as $key => $item) {
   $arr[$item['id']][$key] = $item;
}

ksort($arr, SORT_NUMERIC);

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