When displaying large datasets in pages — or processing records in batches — you need to split an array into fixed-size chunks. Ruby’s each_slice handles this cleanly without manual index arithmetic.

Description

Enumerable#each_slice(n) yields sub-arrays of size n in sequence. The last chunk may be smaller if the total count isn’t evenly divisible. Combined with a page number and page size, you can implement pagination without any gem. This pattern is useful for batching API calls, processing CSV rows in chunks, or building a manual pagination layer over an in-memory collection.

Sample input:

  items = (1..25).to_a
  page = 2
  per_page = 10

Sample Output:

  [11, 12, 13, 14, 15, 16, 17, 18, 19, 20]

Answer

  def paginate(array, page:, per_page:)
    array.each_slice(per_page).to_a[page - 1] || []
  end

  items = (1..25).to_a

  paginate(items, page: 1, per_page: 10)  # => [1..10]
  paginate(items, page: 2, per_page: 10)  # => [11..20]
  paginate(items, page: 3, per_page: 10)  # => [21, 22, 23, 24, 25]
  paginate(items, page: 4, per_page: 10)  # => []

  # Process in batches without page numbers
  items.each_slice(10) do |batch|
    process_batch(batch)
  end

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