php - Group data in csv rows by one column and create comma-separated values from other columns within each group

Solution:

Let you loaded data from CSV to plain array. After this you can applyarray_reduce in next way:

$res = array_reduce(
        $rows,
        function($res, $row) {
            if (isset($res[$row[0]])) {
                $res[$row[0]][1] .= ", $row[1]";
                $res[$row[0]][2] .= ", $row[2]";
                $res[$row[0]][3] .= ", $row[3]";
            }
            else $res[$row[0]] = $row;
            return $res;
        },
        []
    );
var_export($res);
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PHPize - run php code online

Solution:

You can process the whole file by grouping the article number and add the properties to each an array. On output you implode them comma delimited.

$csv = <<<'_CSV'
ArtNo,Name,Color,Size
DEF270, Fingal, Stellar, 3XL
DEF270, Fingal, White, 4XL;
_CSV;

$csv_handle = fopen('php://memory', 'rw');
$fwrite     = fwrite($csv_handle, $csv);
fseek($csv_handle, 0);

$articles = [];
while (($data = fgetcsv($csv_handle)) !== false) {
    [$articleNumber, $name, $color, $size] = array_map('trim', $data);
    if (!isset($articles[$articleNumber])) {
        $articles[$articleNumber] = [
            'names'  => [$name],
            'colors' => [$color],
            'sizes'  => [$size],
        ];
        continue;
    }
    $article = &$articles[$articleNumber];
    if (!in_array($name, $article['names'])) {
        $article['names'][] = $name;
    }
    if (!in_array($color, $article['colors'])) {
        $article['colors'][] = $color;
    }
    if (!in_array($size, $article['sizes'])) {
        $article['sizes'][] = $size;
    }
    unset ($article);
}
fclose($csv_handle);

echo "<table>\n";
foreach ($articles as $articleNumber => $article) {
    $names  = implode(', ', $article['names']);
    $colors = implode(', ', $article['colors']);
    $sizes  = implode(', ', $article['sizes']);
    echo "<tr><td>$articleNumber</td><td>$names</td><td>$colors</td><td>$sizes</tr>\n";
}
echo "</table>\n";
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Output

<table>
<tr><td>ArtNo</td><td>Name</td><td>Color</td><td>Size</tr>
<tr><td>DEF270</td><td>Fingal</td><td>Stellar, White</td><td>3XL, 4XL;</tr>
</table>
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