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How can I add styling to the header in a CSV file using the League\Csv library?

September 18, 2023

I’m currently using the League\Csv library in PHP to generate a CSV file from data in my application. I’d like to add styling (such as bold font or text color) to the header in the generated CSV file to make it stand out when opened in spreadsheet applications like Microsoft Excel.

Currently, I’m using the following PHP code to generate the CSV file:

public function export_data_as_csv() {
        $projectFeature     = new ProjectSingle();
        $role_label         = $projectFeature->role_label;
        
        $estimations = $projectFeature->getEstimations($_POST['project_id']);
        
        // Instantiate a CSV object
        $csv = Writer::createFromString('');
        
        // Header CSV
        $header = [
            'Name', 
            'Est. Hours', 
            'Estimator', 
            'Assigned', 
            'Note', 
            'Problem'
        ];
        $csv->insertOne($header);

        $total_estimation = 0;
        foreach ($estimations as $division => $estimation) {
            if (!empty($estimation)) {
                // Grup parent
                $parent_data = [
                    $role_label[$division],
                    $estimation['post_estimation'],
                    $estimation['estimator'],
                    '', // Assigned
                    '', // Note
                    '', // Problem
                ];
                $csv->insertOne($parent_data);

                foreach ($estimation['timeline'] as $task_name => $timeline) {
                    // Grup konten
                    $content_data = [
                        $task_name,
                        $timeline['est_hours'],
                        '', // Estimator
                        $timeline['est_assigned'],
                        $timeline['est_notes'],
                        $timeline['problems_url'],
                    ];
                    $csv->insertOne($content_data);
                }

                $total_estimation += $estimation['post_estimation'];
            }
        }
        
        $total = ['TOTAL', $total_estimation, '', '', '', ''];
        $csv->insertOne($total);
        
        $file_name = $_POST['project_name'] . '-estimation.csv';
        // $csv->output($file_name);

        $csvData = $csv->toString(); // Get CSV data as a string
        header('Content-Type: text/csv');
        header('Content-Disposition: attachment; filename="' . $file_name . '"');
        echo $csvData;
        $_POST = [];
        exit();
    }

However, the header is displayed as plain text without any special styling. How can I add styling to the header in the generated CSV file?

What I’ve Tried:

I’ve reviewed the documentation for the League\Csv library but couldn’t find information on adding styles to headers.
I’ve attempted to use HTML tags like and <span style="font-weight:bold;"> in the header, but they didn’t work when opened in Excel.

What I Expected:

I expected that there might be a way to apply styles or formatting to the header in the CSV file using the League\Csv library or some other approach. My goal is to have the header text appear bold when the CSV file is opened in Excel.