Ultra Fast Excel Writter for Ruby

require 'fast_excel'

workbook = FastExcel.open("hello_world_ffi.xlsx", constant_memory: true)
  font_size: 0, # user's default
  font_family: "Arial"

worksheet = workbook.add_worksheet("Example Report")

bold = workbook.bold_cell_format
worksheet.set_column(0, 0, FastExcel::DEF_COL_WIDTH, bold)

price = workbook.number_format("#,##0.00")
worksheet.set_column(1, 1, 20, price)

date_format = workbook.number_format("[$-409]m/d/yy h:mm AM/PM;@")
worksheet.set_column(2, 2, 20, date_format)

worksheet.write_row(0, ["message", "price", "date"], bold)

for i in 1..1000
  worksheet.write_row(i, ["Hello", (rand * 10_000_000).round(2), Time.now])

worksheet.write_row(1001, ["Sum", FastExcel::Formula.new("SUM(B2:B1001)")], bold)


This repository and gem contain sources of libxlsxwriter


1000 rows:

           FastExcel:       31.7 i/s
               Axlsx:        8.0 i/s - 3.98x  slower
          write_xlsx:        6.9 i/s - 4.62x  slower

20000 rows:

           FastExcel:        1.4 i/s
               Axlsx:        0.4 i/s - 3.46x  slower
          write_xlsx:        0.1 i/s - 17.04x  slower

Max memory usage, generating 100k rows:

FastExcel   - 20 MB
Axlsx       - 60 MB
write_xlsx - 100 MB


# Gemfile
gem 'fast_excel'


gem install fast_excel


This gem is FFI binding for libxlsxwriter C library with some syntax sugar. All original functions is avaliable, for example:

Libxlsxwriter.worksheet_activate(worksheet) # => will call void worksheet_activate(lxw_worksheet *worksheet)
# or shorter:

Full libxlsxwriter documentation: http://libxlsxwriter.github.io/

Helper Methods:

  • FastExcel.open(filename = nil, constant_memory: false, default_format: {}) - open new workbook, if filename is nil - it will create tmp file, default_format will be called with workbook.default_format.set(...)
  • FastExcel.date_num(time, offset = nil) - generate Excel's internal date value, number of days since 1900-Jan-01, works faster then creating Libxlsxwriter::Datetime struct. offset argument is number hours from UTC, e.g. 3.5
  • FastExcel.print_ffi_obj(object) - print FFI object fields, just for debugging
  • workbook.bold_cell_format - shortcut for creating bold format
  • workbook.number_format(num_format) - create number or date format, for money usually: "#,##0.00", for date: "[$-409]m/d/yy h:mm AM/PM;@"
  • workbook.read_string - close workbook, read file to string, delete file (only if tmp file)
  • workbook.remove_tmp_file - delete tmp file (only if tmp file)
  • worksheet.write_row(row_num, array_of_mixed_value, formats = nil) - write values one by one, detecting type automatically. formats can be array, or Format object or nil
  • format.font_family - alias for format.font_name
  • workbook.default_format.font_size - set it to 0 if you want to use default font size (that what user set in Excel settings)