offset.md

Offset

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The offset operation skips a specified number of rows from the beginning of the dataset, commonly used for pagination and data sampling.

Basic Offset Usage

offset() - Skip rows from beginning

<?php

use function Flow\ETL\DSL\{data_frame, from_array, to_output};

$dataFrame = data_frame()
    ->read(from_array([
        ['id' => 1, 'name' => 'Alice'],
        ['id' => 2, 'name' => 'Bob'],
        ['id' => 3, 'name' => 'Charlie'],
        ['id' => 4, 'name' => 'David'],
        ['id' => 5, 'name' => 'Eve'],
    ]))
    ->offset(2) // Skip first 2 rows
    ->write(to_output())
    ->run();

// Output: Charlie, David, Eve

Performance Considerations

⚠️ Performance Warning: The offset() method must iterate through and process all skipped rows to reach the offset position. For large offsets (e.g., offset(1000000)), this can significantly impact performance as the DataFrame still needs to read and process all data up to the offset point.