How to Eliminate Redundant Code: A Practical DRY Refactoring Guide in PHP

Do Not Repeat Yourself (DRY) is a fundamental software development principle that aims to eliminate duplicated code.

The original Report class prints report data directly in the show method, and a later requirement to save the report to a file leads to duplicated logic.

class Report {
    public function show(array $data) {
        echo "Report: " . ucwords(strtolower($data["name"])) . "
";
        echo "Product: " . ucwords(strtolower($data["product"])) . "
";
        echo "Start date: " . date("Y/m/d", $data["startDate"]) . "
";
        echo "End date: " . date("Y/m/d", $data["endDate"]) . "
";
        echo "Total: " . $data["total"] . "
";
        echo "Average x day: " . floor($data["total"] / 365) . "
";
        echo "Average x week: " . floor($data["total"] / 52) . "
";
    }
}

When a new saveToFile method is added, the same printing logic is duplicated, violating DRY.

class Report {
    public function saveToFile(array $data) {
        echo "Report: " . ucwords(strtolower($data["name"])) . "
";
        // ... same duplicated code ...
        file_put_contents("./report.txt", $report);
    }
}

Refactoring extracts the common report‑building code into a private createReport method, which both show and saveToFile call.

class Report {
    public function show(array $data) {
        echo $this->createReport($data);
    }
    public function saveToFile(array $data) {
        file_put_contents("./report.txt", $this->createReport($data));
    }
    private function createReport(array $data): string {
        $report = '';
        $report .= "Report: " . ucwords(strtolower($data["name"])) . "
";
        $report .= "Product: " . ucwords(strtolower($data["product"])) . "
";
        $report .= "Start date: " . date("Y/m/d", $data["startDate"]) . "
";
        $report .= "End date: " . date("Y/m/d", $data["endDate"]) . "
";
        $report .= "Total: " . $data["total"] . "
";
        $report .= "Average x day: " . floor($data["total"] / 365) . "
";
        $report .= "Average x week: " . floor($data["total"] / 52) . "
";
        return $report;
    }
}

Further duplication (name formatting, date formatting, average calculations) is removed by adding helper methods normalizeName, formatDate, and calculateAverage.

private function normalizeName($name): string {
    return ucwords(strtolower($name));
}
private function formatDate($date): string {
    return date("Y/m/d", $date);
}
private function calculateAverage(array $data, $period): string {
    return floor($data["total"] / $period);
}

The final refactored Report class combines these helpers, resulting in concise, reusable code that adheres to the DRY principle.

class Report {
    public function show(array $data) {
        echo $this->createReport($data);
    }
    public function saveToFile(array $data) {
        file_put_contents("./report.txt", $this->createReport($data));
    }
    private function createReport(array $data) {
        $report = '';
        $report .= "Report: " . $this->normalizeName($data["name"]) . "
";
        $report .= "Product: " . $this->normalizeName($data["product"]) . "
";
        $report .= "Start date: " . $this->formatDate($data["startDate"]) . "
";
        $report .= "End date: " . $this->formatDate($data["endDate"]) . "
";
        $report .= "Total: " . $data["total"] . "
";
        $report .= "Average x day: " . $this->calculateAverage($data, 365) . "
";
        $report .= "Average x week: " . $this->calculateAverage($data, 52) . "
";
        $report .= "Average x month: " . $this->calculateAverage($data, 12) . "
";
        return $report;
    }
    private function formatDate($date): string {
        return date("Y/m/d", $date);
    }
    private function calculateAverage(array $data, $period): string {
        return floor($data["total"] / $period);
    }
    private function normalizeName($name): string {
        return ucwords(strtolower($name));
    }
}

Applying DRY throughout the codebase improves readability, reduces maintenance effort, and helps developers build more robust software.