traversable_operator.php

<?php

interface TraversableOperatorInterface
{
    /**
     * @param Traversable $rows
     * @param callable $callable
     * @return Generator
     */
    public function append(Traversable $rows, callable $callable);

    /**
     * @param Traversable $rows
     * @param callable $callable
     * @return Generator
     */
    public function map(Traversable $rows, callable $callable);
}

class TraversableOperator
{
    /**
     * @param Traversable $rows
     * @param callable $callable (return Traversable)
     * @return Generator
     */
    public function append(Traversable $rows, callable $callable)
    {
        foreach ($rows as $key => $row) {
            $result = call_user_func($callable, $row);

            if (!$result instanceof Traversable) {
                throw new \LogicException('Callable must return array or Traversable:' . gettype($result));
            }

            yield $key => array_merge($row, iterator_to_array($result));
        }
    }

    /**
     * @param Traversable $rows
     * @param callable $callable
     * @return Generator
     */
    public function map(array $rows, callable $callable)
    {
        foreach ($rows as $key => $row) {
            yield $key => array_map($callable, $row);
        }
    }
}

class Calculator
{
    /**
     * @param array $row
     * @return Traversable
     */
    public function calculate(array $row)
    {
        yield 'rate' => $row['click'] / $row['imp'];
    }
}

$rows = [
     0 => ['id' => 1, 'imp' => 100, 'click' => 0],
     2 => ['id' => 2, 'imp' => 200, 'click' => 1],
     4 => ['id' => 3, 'imp' => 300, 'click' => 2],
     8 => ['id' => 4, 'imp' => 400, 'click' => 4],
    16 => ['id' => 5, 'imp' => 500, 'click' => 8],
];


$operator = new TraversableOperator;

$rows = new ArrayIterator($rows);

// naming
$rows = $operator->append($rows, function(array $row) {
    yield 'name' => "id={$row['id']}";
});

// calculating
$rows = $operator->append($rows, [new Calculator, 'calculate']);

var_dump(iterator_to_array($rows));