Combine object values in a single array by matching object fields in PHP

Question

I've been digging around and trying to solve this issue the cleanest way possible, but haven't quite found the right approach.

I have an array of objects like so:

$myArray = [
    {field: "Diameter", measurement: 15, count: 4},
    {field: "Diameter", measurement: 16, count: 1},
    {field: "Diameter", measurement: 17, count: 15},
    {field: "Width", measurement: 7, count: 12},
    {field: "Width", measurement: 8, count: 8},
    {field: "Brands", measurement: "blah", count: 1},
    {field: "Brands", measurement: "doubleBlah", count: 3},
    {field: "Brands", measurement: "blah", count: 1},
    {field: "Brands", measurement: "doubleBlah", count: 3},
    {field: "Brands", measurement: "blah", count: 12}
    ]

and I need to combine the objects that have duplicate measurement fields and combine the counts like this:

$myBetterArray = [
    {field: "Diameter", measurement: 15, count: 4},
    {field: "Diameter", measurement: 16, count: 1},
    {field: "Diameter", measurement: 17, count: 15},
    {field: "Width", measurement: 7, count: 12},
    {field: "Width", measurement: 8, count: 8},
    {field: "Brands", measurement: "blah", count: 14},
    {field: "Brands", measurement: "doubleBlah", count: 6},
    ]

can it be done with something like array_map or something equally clean and not too verbose? Any help would be much appreciated.

Torbjörn Stabo · Accepted Answer · 2020-10-04 12:30:08Z

1

Based on the keys being "hidden" like that, the data format known, and the way the question is written('the cleanest way possible', 'not too verbose') I'd simply go for foreach():

$myArray = '[
{"field": "Diameter", "measurement": 15, "count": 4},
{"field": "Diameter", "measurement": 16, "count": 1},
{"field": "Diameter", "measurement": 17, "count": 15},
{"field": "Width", "measurement": 7, "count": 12},
{"field": "Width", "measurement": 8, "count": 8},
{"field": "Brands", "measurement": "blah", "count": 1},
{"field": "Brands", "measurement": "doubleBlah", "count": 3},
{"field": "Brands", "measurement": "blah", "count": 1},
{"field": "Brands", "measurement": "doubleBlah", "count": 3},
{"field": "Brands", "measurement": "blah", "count": 12}
]';
$myArray = json_decode($myArray);

// Sort the data
$_im = [];
foreach($myArray as $item) {
    $_im[$item->field][$item->measurement] = $item->count + ($_im[$item->field][$item->measurement] ?? 0);
}

// Output it in the desired format
$res = [];
foreach($_im as $field => $fdata) {
    foreach($fdata as $measurement => $count) {
        $res []= (object) compact('field', 'measurement', 'count');
    }
}

print_r($res);

Process the data in an intermediary array where you can use the keys(if you don't do it that way searching for a given pair of keys later would be more complex), and then another foreach to put the result together in the desired format.

This should be enough for 2 levels. Also, it might be nice to put the code in a function to keep $_im from polluting the namespace.

(object) [] is a simple way to cast an array into an object(stdClass), since that seems to be the format of the data in the question.

?? 0 creates a start value for the case when the current $_im[$item->field][$item->measurement] isn't there yet (i.e. each time there's a new field,measurement pair). Shorter to write than using isset().

edited Oct 4, 2020 at 12:30

answered Oct 3, 2020 at 1:00

Torbjörn Stabo

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4 Comments

LSerni Over a year ago

I can't seem to run this code on PHP 7.4.3. It works if I replace the compact() with $res[]= [ 'field' => $field, 'measurement' => $measurement, 'count' => $count ]; (I still get several E_NOTICE messages)

Torbjörn Stabo Over a year ago

@LSerni My bad, compact() wants the variable names, not the variables themselves.

BRose Over a year ago

I had to change this line to this: $_im[$item['field']][$item['measurement']] = $item['count'] + ($_im[$item['field']][$item['measurement']] ?? 0); but that did the trick and it wasn't too verbose, thank you!

Torbjörn Stabo Over a year ago

@BRose Ok, so $item is an array, not an object? Sorry, I misinterpreted the data then. Glad it worked!

LSerni · Accepted Answer · 2020-10-03 12:10:26Z

First sort the array so that all measurements to be possibly connected are contiguous; this will allow you to only check contiguous elements.

This approach makes it easier to change the field specification (also called signature or syndrome) of each record, uses less memory and is resistant to the "Schlemiel the Painter" problem in case of very long arrays.

$keys = [ 'field', 'measurement' ];

uasort($array, function($item1, $item2) use ($keys) {
    foreach ($keys as $key) {
        if ($item1[$key] === $item2[$key]) {
            continue;
        }
        if ($item1[$key] < $item2[$key]) {
            return -1;
        }
        return 1;
    }
    return 0;
});
// This is to be sure that the array will reencode as a JSON array
$array = array_values($array);

Now your array should look like this:

 [
    {"field":"Brands","measurement":"blah","count":1},
    {"field":"Brands","measurement":"blah","count":1},
    {"field":"Brands","measurement":"blah","count":12},
    {"field":"Brands","measurement":"doubleBlah","count":3},
    {"field":"Brands","measurement":"doubleBlah","count":3},
    {"field":"Diameter","measurement":15,"count":4},
    {"field":"Diameter","measurement":16,"count":1},
    {"field":"Diameter","measurement":17,"count":15},
    {"field":"Width","measurement":7,"count":12},
    {"field":"Width","measurement":8,"count":8}
 ]

Now, scan the array coalescing the counts with the same key-syndrome.

$j = -1;
$advance = true;
foreach ($array as $i => $row) {
    if ($j >= 0) {
        $advance = false;
        foreach ($keys as $key) {
            if ($array[$i][$key] !== $array[$j][$key]) {
                $advance = true;
                break;
            }
        }
        if (!$advance) {
            // Row $i is a duplicate of row $j
            $array[$j]['count'] += $array[$i]['count'];
        }
    }
    if ($advance) {
        // Row $i is moved in row $j
        $j++;
        if ($j !== $i) {
            $array[$j] = $array[$i];
        }
    }
}
// All rows past j must be deleted
$array = array_slice($array, 0, $j+1);

Array is now:

[
    {"field":"Brands","measurement":"blah","count":14},
    {"field":"Brands","measurement":"doubleBlah","count":6},
    {"field":"Diameter","measurement":15,"count":4},
    {"field":"Diameter","measurement":16,"count":1},
    {"field":"Diameter","measurement":17,"count":15},
    {"field":"Width","measurement":7,"count":12},
    {"field":"Width","measurement":8,"count":8}
]

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