A long-lived project that still receives updates
Useful extensions to Date, String, Range and other classes



 Project Readme


fat-core is a simple gem to collect core extensions and a few new classes that I find useful in multiple projects. The emphasis is on extending the Date class to make it more useful in financial applications.


Add this line to your application’s Gemfile:

gem 'fat_core', :git => ''

And then execute:

$ bundle

Or install it yourself as:

$ gem install fat_core


You can extend classes individually by requiring the corresponding file:

require 'fat_core/array'
require 'fat_core/bigdecimal'
require 'fat_core/date'
require 'fat_core/enumerable'
require 'fat_core/hash'
require 'fat_core/kernel'
require 'fat_core/numeric'
require 'fat_core/range'
require 'fat_core/string'
require 'fat_core/symbol'

Or, you can require them all:

require 'fat_core/all'

Many of these have little that is of general interest, but there are a few goodies.



FatCore adds two constants to the Date class, Date::BOT and Date::EOT. These represent the earliest and latest dates of practical commercial interest. The exact values are rather arbitrary, but they prove useful in date ranges, for example. They are defined as:

January 1, 1900
December 31, 3000
an Array of dates declared as non-work days for federal employees by presidential proclamation
an Array of dates of presidential funerals, which are observed with a closing of most federal agencies


FatCore provides some concise methods for printing string versions of dates that are often useful:

require 'fat_core/date'
d = Date.parse('1957-09-22')
puts "ISO: #{d.iso}"
puts "All Numbers: #{d.num}"
puts "Emacs Org Mode Inactive: #{}"
puts "Emacs Org Mode Active: #{}"
puts "LaTeX: #{d.tex_quote}"
puts "English: #{d.eng}"
puts "American: #{d.american}"
ISO: 1957-09-22
All Numbers: 19570922
Emacs Org Mode Inactive: [1957-09-22 Sun]
Emacs Org Mode Active: <1957-09-22 Sun>
LaTeX: 1957--09--22
English: September 22, 1957
American: 9/22/1957

Most of these are self-explanatory, but a couple are not. The #org method formats a date as an Emacs org-mode timestamp, by default an inactive timestamp that does not show up in the org agenda, but can be made active with the optional parameter set to a truthy value. See

The #tex_quote method formats the date in iso form but using TeX’s convention of using en-dashes to separate the components.


Many of the methods provided by FatCore deal with various calendar periods that are less common than those provided by the Ruby Standard Library or gems such as active_suupor. This documentation refers to these calendar periods as “chunks”, and they are the following:

  • year,
  • half,
  • quarter,
  • bimonth,
  • month,
  • semimonth,
  • biweek,
  • week, and
  • day

FatCore provides methods that query whether the date falls on the beginning or end of each of these chunks:

require 'fat_core/date'

tab = []
d = Date.parse('2017-06-30')
%i[beginning end].each do |side|
  %i(year half quarter bimonth month semimonth biweek week ).each do |chunk|
    meth = "#{side}_of_#{chunk}?".to_sym
    tab << [d.iso, meth.to_s, "#{d.send(meth)}"]
| 2017-06-30 | beginning_of_year?      | false |
| 2017-06-30 | beginning_of_half?      | false |
| 2017-06-30 | beginning_of_quarter?   | false |
| 2017-06-30 | beginning_of_bimonth?   | false |
| 2017-06-30 | beginning_of_month?     | false |
| 2017-06-30 | beginning_of_semimonth? | false |
| 2017-06-30 | beginning_of_biweek?    | false |
| 2017-06-30 | beginning_of_week?      | false |
| 2017-06-30 | end_of_year?            | false |
| 2017-06-30 | end_of_half?            | true  |
| 2017-06-30 | end_of_quarter?         | true  |
| 2017-06-30 | end_of_bimonth?         | true  |
| 2017-06-30 | end_of_month?           | true  |
| 2017-06-30 | end_of_semimonth?       | true  |
| 2017-06-30 | end_of_biweek?          | false |
| 2017-06-30 | end_of_week?            | false |

It also provides corresponding methods that return the date at the beginning or end of the calendar chunk, starting at the given date:

require 'fat_core/date'

tab = []
d = Date.parse('2017-04-21')
%i[beginning end].each do |side|
  %i(year half quarter bimonth month semimonth biweek week ).each do |chunk|
    meth = "#{side}_of_#{chunk}".to_sym
    tab << [d.iso, "d.#{meth}", "#{d.send(meth)}"]
| 2017-04-21 | d.beginning_of_year      | 2017-01-01 |
| 2017-04-21 | d.beginning_of_half      | 2017-01-01 |
| 2017-04-21 | d.beginning_of_quarter   | 2017-04-01 |
| 2017-04-21 | d.beginning_of_bimonth   | 2017-03-01 |
| 2017-04-21 | d.beginning_of_month     | 2017-04-01 |
| 2017-04-21 | d.beginning_of_semimonth | 2017-04-16 |
| 2017-04-21 | d.beginning_of_biweek    | 2017-04-10 |
| 2017-04-21 | d.beginning_of_week      | 2017-04-17 |
| 2017-04-21 | d.end_of_year            | 2017-12-31 |
| 2017-04-21 | d.end_of_half            | 2017-06-30 |
| 2017-04-21 | d.end_of_quarter         | 2017-06-30 |
| 2017-04-21 | d.end_of_bimonth         | 2017-04-30 |
| 2017-04-21 | d.end_of_month           | 2017-04-30 |
| 2017-04-21 | d.end_of_semimonth       | 2017-04-30 |
| 2017-04-21 | d.end_of_biweek          | 2017-04-23 |
| 2017-04-21 | d.end_of_week            | 2017-04-23 |

You can query which numerical half, quarter, etc. that a given date falls in:

require 'fat_core/date'

tab = []
%i(year half quarter bimonth month semimonth biweek week ).each do |chunk|
  d = Date.parse('2017-04-21') + rand(100)
  meth = "#{chunk}".to_sym
  tab << [d.iso, "d.#{meth}", "in #{chunk} number #{d.send(meth)}"]
| 2017-07-05 | d.year      | in year number 2017   |
| 2017-06-03 | d.half      | in half number 1      |
| 2017-05-30 | d.quarter   | in quarter number 2   |
| 2017-07-08 | d.bimonth   | in bimonth number 4   |
| 2017-06-28 | d.month     | in month number 6     |
| 2017-05-14 | d.semimonth | in semimonth number 9 |
| 2017-07-25 | d.biweek    | in biweek number 15   |
| 2017-06-19 | d.week      | in week number 25     |


FatCore also adds some convenience methods for parsing strings as Date objects.

American Dates

Americans often write dates in the form M/d/Y, and the normal parse method will parse such a string as d/M/Y, often resulting in invalid date errors. FatCore adds the specialty parsing method, Date.parse_american to handle such strings.

require 'fat_core/date'

  ss = '9/22/1957'
rescue Date::Error => ex
  puts "Date.parse('#{ss}') raises #{ex.class} (#{ex}), but"
  puts "Date.parse_american('#{ss}') => #{Date.parse_american(ss)}"
Date.parse('9/22/1957') raises Date::Error (invalid date), but
Date.parse_american('9/22/1957') => 1957-09-22
Date Specs

Holidays and Workdays

  • weekend?
  • weekday?

Weekdays in Month


The Date class extension adds two methods for determining whether a given date is a US federal holiday as defined by federal law, including such things as federal holidays established by executive decree:

require 'fat_core/date'
Date.parse('2014-05-18').fed_holiday?  => true # It's a weekend
Date.parse('2014-01-01').fed_holiday?  => true # It's New Years

Likewise, days on which the NYSE is closed can be gotten with:

Date.parse('2014-04-18').nyse_holiday? => true # It's Good Friday

Conversely, Date#fed_workday? and Date#nyse_workday? return true if the federal government and the NYSE respectively are open for business on those days.

In addition, the Date class, as extended by FatCore, adds #next_<chunk> methods for calendar periods in addition to those provided by the core Date class: #next_half, #next_quarter, #next_bimonth, and #next_semimonth, #next_biweek. There are also #prior_<chunk> variants of these, as well as methods for finding the end and beginning of all these periods (e.g., #beginning_of_bimonth) and for querying whether a Date is at the beginning or end of these periods (e.g., #beginning_of_bimonth?, #end_of_bimonth?, etc.).

FatCore also provides convenience formatting methods, such as Date#iso for quickly converting a Date to a string of the form ‘YYYY-MM-DD’, Date#org for formatting a Date as an Emacs org-mode timestamp, and several others.

Finally, it provides a #parse_spec method for parsing a string, typically provided by a user, allowing all the period chunks to be conveniently and tersely specified by a user. For example, the string ‘2Q’ will be parsed as the second calendar quarter of the current year, while ‘2014-3Q’ will be parsed as the third quarter of the year 2014.


You can also extend the Range class with several useful methods that emphasize coverage of one range by one or more others (#spanned_by? and #gaps), contiguity of Ranges to one another (#contiguous?, #left_contiguous?, and #right_contiguous?, #join), and the testing of overlaps between ranges (#overlaps?, #overlaps_among?). These are put to good use in the ‘fat_period’ ( gem, which combines fat_core’s extended Range class with its extended Date class to make a useful Period class for date ranges, and you may find fat_core’s extended Range class likewise useful.

For example, you can use the #gaps method to find the gaps left in the coverage on one Range by an Array of other Ranges:

require 'fat_core/range'
(0..12).gaps([(0..2), (5..7), (10..12)])  => [(3..4), (8..9)]



FatCore::Enumerable extends Enumerable with the #each_with_flags method that yields the elements of the Enumerable but also yields two booleans, first and last that are set to true on respectively, the first and last element of the Enumerable. This makes it easy to treat these two cases specially without testing the index as in #each_with_index.


FatCore::Hash extends the Hash class with some useful methods for element deletion (#delete_with_value) and for manipulating the keys (#keys_with_value, #remap_keys and #replace_keys) of a Hash. It also provides #each_pair_with_flags as an analog to Enumerable’s #each_with_flags.


FatCore::String has methods for performing matching of one string with another (#matches_with, #fuzzy_match), for converting a string to title-case as might by used in the title of a book (#entitle), for converting a String into a useable Symbol (#as_sym) and vice-versa (#as_string also Symbol#as_string), for wrapping with an optional hanging indent (#wrap), cleaning up errant spaces (#clean), and computing the Damerau-Levenshtein distance between strings (#distance). And several others.

TeX Quoting

Several of the extension, most notably ‘fat_core/string’, provides a #tex_quote method for quoting the string version of an object so as to allow its inclusion in a TeX document and quote characters such as ‘$’ or ‘%’ that have a special meaning for TeX.


FatCore::Numeric has methods for inserting grouping commas into a number (#commas and #group), for converting seconds to HH:MM:SS.dd format (#secs_to_hms), for testing for integrality (#whole? and #int_if_whole), and testing for sign (#signum).


  1. Fork it ( )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (~git commit -am ‘Add some feature’~)
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request