Change background color of a cell when next value is different from the preceding one

I’ve been around for years on Stack but this is my first time posting. I’m working on a website (php + mysql) and the following problem is driving me absolutely nuts.

I have a table with 2 columns: Size and Amount. The table is generated by a basic php script simply outputting values stored in the database as rows in the table. Super basic, no fancy stuff there:

SELECT Size, Amount FROM database WHERE product = 'product123' ORDER BY Size ASC

The php echo outputs an html table displaying Size and the corresponding available packs (Amount).

Echo '<td>'.$record['size'].'</td><td>'.$record['amount'].'</td>'

Some Sizes are available in different Amounts, so therefore a particular Size can appear multiple times. Example:

Size | Amount
1    | 10
1    | 50
2    | 10
2+   | 10
3    | 40
3+   | 25
3+   | 40
4+   | 25

What I’m looking to achieve is that rows containing the same Size have the same background color. So it should alternate, grouped by Size, and this is irregular unfortunately. Example:

Size | Amount
1    | 10     < yellow
1    | 50     < yellow
2    | 10     < transparent
2+   | 10     < yellow
3    | 40     < transparent
3+   | 25     < yellow
3+   | 40     < yellow
4+   | 25     < transparent

So if the next Size is different from the preceding one, the row background color should change. This way a single Size is alternately highlighted as a group. Note that Size 2 and 2+ (same for 3 and 3+) are considered to be different sizes, hence the background color should change.

I can’t figure out how to achieve this with php. The difficulty is that I can’t use an evaluation based on odd/even since there sometimes is a “+” involved, making not all Sizes numeric values. Changing the naming scheme to get rid of that “+” is not an option unfortunately.

I was thinking of somehow having php check, while generating the table row by row, if the next outputted Size is identical to the preceding one. If yes: no change in bg-color. If no: change bg-color. However I can’t figure out what the best way is to code something like this. Any pointers in the right direction are much appreciated.

Answer

Just a MCVE:

// your data
$records[] = array('size' => "1");
$records[] = array('size' => "1");
$records[] = array('size' => "2");
$records[] = array('size' => "2+");
$records[] = array('size' => "3");
$records[] = array('size' => "3+");
$records[] = array('size' => "3+");
$records[] = array('size' => "4");

$lastSize = $records[0]['size'];
$color = "yellow";

foreach ($records as $record) {
    if ($lastSize != $record['size']) {
        $lastSize = $record['size'];
        if ($color == "yellow") $color = "transparent";
        else $color = "yellow";
    }
    $lastSize == $record['size'];
    echo $record['size'].' - '.$color.'<br>';
}

// OUTPUT:
// 1 - yellow
// 1 - yellow
// 2 - transparent
// 2+ - yellow
// 3 - transparent
// 3+ - yellow
// 3+ - yellow
// 4 - transparent