The row_number() function assigns a unique sequential number to each row within a partition, starting at 1. Unlike rank() and dense_rank(), row_number() always assigns different numbers to each row, even when values are tied.
This is useful for pagination, selecting top N rows per group, or creating unique identifiers within partitions.
Window functions compute over a frame of rows without collapsing them.
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<?php
declare(strict_types=1);
use function Flow\ETL\DSL\{data_frame, row_number, from_array, ref, to_output, window};
require __DIR__ . '/vendor/autoload.php';
$df = data_frame()
->read(
from_array([
['id' => 1, 'name' => 'Greg', 'department' => 'IT', 'salary' => 6000],
['id' => 2, 'name' => 'Michal', 'department' => 'IT', 'salary' => 5000],
['id' => 3, 'name' => 'Tomas', 'department' => 'Finances', 'salary' => 11_000],
['id' => 4, 'name' => 'John', 'department' => 'Finances', 'salary' => 9000],
['id' => 5, 'name' => 'Jane', 'department' => 'Finances', 'salary' => 14_000],
['id' => 6, 'name' => 'Janet', 'department' => 'Finances', 'salary' => 9000],
])
)
->withEntry('row_num', row_number()->over(window()->partitionBy(ref('department'))->orderBy(ref('salary')->desc())))
->sortBy([ref('department'), ref('row_num')])
->collect()
->write(to_output(truncate: false))
->run();
