Number and currency localization and formatting functions for the Common Locale Data Repository (CLDR).


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Number and Currency Localization and Formatting

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Introduction and Getting Started

ex_cldr_numbers is an addon library application for ex_cldr that provides localization and formatting for numbers and currencies.

In order to use this library, a backend module for ex_cldr must be defined. This is described in full in the ex_cldr readme. To get started immediate, define a module in your project as follows:

defmodule MyApp.Cldr do
  use Cldr, locales: ["en", "fr", "zh"]
end

The following examples assume the existence of this module.

The primary api is MyApp.Cldr.Number.to_string/2. The following examples demonstrate:

iex> MyApp.Cldr.Number.to_string 12345
{:ok, "12,345"}

iex> MyApp.Cldr.Number.to_string 12345, locale: "fr"
{:ok, "12 345"}

iex> MyApp.Cldr.Number.to_string 12345, locale: "fr", currency: "USD"
{:ok, "12 345,00 $US"}

iex> MyApp.Cldr.Number.to_string 12345, format: "#E0"
{:ok, "1.2345E4"}

For help in iex:

iex> h MyApp.Cldr.Number.to_string

Known restrictions and limitations

Unicode technical report TR35 states that for scientific formats (i.e. mantissa and exponent):

The maximum number of integer digits, if present, specifies the exponent grouping. The most common use of this is to generate engineering notation, in which the exponent is a multiple of three, for example, "##0.###E0". The number 12345 is formatted using "##0.####E0" as "12.345E3".

ex_cldr_numbers does not currently support this functionality.

Installation

Note that ex_cldr_numbers requires Elixir 1.5 or later.

Add ex_cldr_numbers as a dependency to your mix project:

defp deps do
  [
    {:ex_cldr_numbers, "~> 2.0"}
  ]
end

then retrieve ex_cldr_numbers from hex:

mix deps.get
mix deps.compile

Configuration

ex_cldr_numbers uses the configuration set for the dependency ex_cldr. See the documentation for ex_cldr

Using Cldr_Numbers

CLDR defines many different ways to format a number for different uses and defines a set of formats categorised by common pupose to make it easier to express the same intent across many different locales that represent many different territories, cultures, number systems and scripts.

See MyApp.Cldr.Number, MyApp.Cldr.Number.to_string/2 and Cldr.Number.to_number_system/3.

Primary Public API

The primary api for number formatting is MyApp.Cldr.Number.to_string/2. It provides the ability to format numbers in a standard way for configured locales. It also provides the means for format numbers as a currency, as a short form (like 1k instead of 1,000). Additionally it provides formats to spell a number in words, format it as roman numerals and output an ordinal number. Some examples illustrate:

iex> MyApp.Cldr.Number.to_string 12345
{:ok, "12,345"}

iex> MyApp.Cldr.Number.to_string 12345, locale: "fr"
{:ok, "12 345"}

iex> MyApp.Cldr.Number.to_string 12345, locale: "fr", currency: "USD"
{:ok, "12 345,00 $US"}

iex> MyApp.Cldr.Number.to_string 12345, format: "#E0"
{:ok, "1.2345E4"}

iex> MyApp.Cldr.Number.to_string 12345, format: :accounting, currency: "THB"
{:ok, "THB12,345.00"}

iex> MyApp.Cldr.Number.to_string -12345, format: :accounting, currency: "THB"
{:ok, "(THB12,345.00)"}

iex> MyApp.Cldr.Number.to_string 12345, format: :accounting, currency: "THB", locale: "th"
{:ok, "THB12,345.00"}

iex> MyApp.Cldr.Number.to_string 12345, format: :accounting, currency: "THB", locale: "th", number_system: :native
{:ok, "THB๑๒,๓๔๕.๐๐"}

iex> MyApp.Cldr.Number.to_string 1244.30, format: :long
{:ok, "1 thousand"}

iex> MyApp.Cldr.Number.to_string 1244.30, format: :long, currency: "USD"
{:ok, "1,244.30 US dollars"}

iex> MyApp.Cldr.Number.to_string 1244.30, format: :short
{:ok, "1K"}

iex> MyApp.Cldr.Number.to_string 1244.30, format: :short, currency: "EUR"
{:ok, "€1.24K"}

iex> MyApp.Cldr.Number.to_string 1234, format: :spellout
{:ok, "one thousand two hundred thirty-four"}

iex> MyApp.Cldr.Number.to_string 1234, format: :spellout_verbose
{:ok, "one thousand two hundred and thirty-four"}

iex> MyApp.Cldr.Number.to_string 123, format: :ordinal
{:ok, "123rd"}

iex> MyApp.Cldr.Number.to_string 123, format: :roman
{:ok, "CXXIII"}

Standard Formatting Styles

Cldr supports the styles of formatting defined by CLDR being:

  • :standard which formats a number if a decimal format commonly used in many locales. This is the default format.
iex> MyApp.Cldr.Number.to_string 1234, format: :standard
{:ok, "1,234"}
  • :currency which formats a number according to the format or a particular currency adjusted for rounding, number of decimal digits after the fraction, whether the currency is accounting or cash rounded and using the appropriate locale-specific currency symbol. This format also requires that the option :currency be specified. Note that for currency formatting the defined rounding and fractional digits defined for the currency is used. The parameter :currency_digits can also be specified to indicate if formatting is to use :accounting, :cash or :iso digit definitions. The default is :accounting. Some currencies, like the Swiss Franc and Australian Dollar have a smallest cash amount that is 0.05 of the Franc of Dollar and hence rouding has to take that into account.
iex> MyApp.Cldr.Number.to_string 1234.31, format: :currency, currency: :CHF
{:ok, "CHF1,234.31"}

iex> MyApp.Cldr.Number.to_string 1234.31, format: :currency, currency: :CHF, currency_digits: :cash
{:ok, "CHF1,234.30"}
  • :accounting which formats a positive number like :standard but which usually wraps a negative number in (). The :accounting format also requires that the :currency option be specified.
iex> MyApp.Cldr.Number.to_string 1234, format: :accounting, currency: :THB
{:ok, "THB1,234.00"}

iex> MyApp.Cldr.Number.to_string -1234, format: :accounting, currency: :THB
{:ok, "(THB1,234.00)"}
  • :percent which multiplies a number by 100 and includes a locale-specific percent symbol which is usually %.
iex> MyApp.Cldr.Number.to_string 0.09, format: :percent
{:ok, "9%"}
  • :permille (aka 'basis points') which multiples a number by 1,000 and includes a locale specific permille symbol which is usually . Note that many (most?) locales don't provide a :permille format definition. The alternative is to specify a format string as in the example below.
iex> MyApp.Cldr.Number.to_string 0.56, format: "#‰"
{:ok, "560‰"}

iex> MyApp.Cldr.Number.to_string 0.56, format: :permille
{:error,
 {MyApp.Cldr.UnknownFormatError,
  "The locale \"en\" with number system :default does not define a format :permille."}}
  • :scientific which formats a number as a mantissa and base-10 exponent.
iex> MyApp.Cldr.Number.to_string 124.56, format: :scientific
{:ok, "1.2456E2"}

See MyApp.Cldr.Number.Formatter.Decimal.

Short and Long Formats

Cldr also supports formats that minimise publishing space or which attempt to make large numbers more human-readable.

  • :short which presents a number or currency in a narrow space.
iex> MyApp.Cldr.Number.to_string 12456.56, format: :short
{:ok, "12K"}

iex> MyApp.Cldr.Number.to_string 12456.56, format: :short, currency: :USD
{:ok, "$12K"}
  • :long which presents numbers in a sentence form adjusted for plurality and locale. For example, 1,0000 would be formatted as 1 thousand. This is not the same as spelling out the number which is part of the Unicode CLDR Rules-Based Number Formatting. See MyApp.Cldr.Rbnf.
iex> MyApp.Cldr.Number.to_string 12456.56, format: :long
{:ok, "12 thousand"}

iex> MyApp.Cldr.Number.to_string 1, format: :long, currency: :USD
{:ok, "1 US dollar"}

iex> MyApp.Cldr.Number.to_string 12456.56, format: :long, currency: :USD
{:ok, "12,457 US dollars"}

See MyApp.Cldr.Number.Formatter.Short and MyApp.Cldr.Number.Formatter.Currency.

User-Specified Number Formats

User-defined decimal formats are also supported using the formats described by Unicode technical report TR35.

The formats described therein are supported by Cldr with some minor omissions and variations. Some examples of number formats are:

Pattern Currency Text
#,##0.## n/a 1 234,57
#,##0.### n/a 1 234,567
###0.##### n/a 1234,567
###0.0000# n/a 1234,5670
00000.0000 n/a 01234,5670
00 n/a 12
#,##0.00 ¤ EUR 1 234,57 €

See MyApp.Cldr.Number and MyApp.Cldr.Number.Formatter.Decimal.

Number Pattern Character Definitions

The folllowing table describes the symbols used in a number format string and is extracted from TR35

Symbol Location Localized Replacement Meaning
0 Number digit Digit
1 .. 9 Number digit '1' through '9' indicate rounding
@ Number digit Significant digit
# Number digit, nothing Digit, omit leading/trailing zeros
. Number decimal symbol Decimal or monetary decimal separator
- Number minus sign Minus sign[1]
, Number grouping separator Decimal/monetary grouping separator[2]
E Number exponent Separates mantissa and exponent for scientific formatting
+ Exponent plus sign Prefix positive exponent with plus sign
% Pre/Suffix percent sign Multiply by 100 and show as a percentage
Pre/Suffix per mille Multiply by 1000 and show as per mille (aka “basis points”)
; Subpattern syntax only Separates positive and negative subpatterns
¤ Pre/Suffix currency symbol Currency symbol[3]
* Pre/Suffix padding character Pad escape, precedes padding character
' Pre/Suffix syntax only To quote special chars. eg '#'

Notes

[1] The pattern '-'0.0 is not the same as the pattern -0.0. In the former case, the minus sign is a literal. In the latter case, it is a special symbol, which is replaced by the localised minus symbol, and can also be replaced by the plus symbol for a format like +12%.

[2] May occur in both the integer part and the fractional part. The position determines the grouping.

[3] Any sequence is replaced by the localized currency symbol for the currency being formatted, as in the table below. If present in a pattern, the monetary decimal separator and grouping separators (if available) are used instead of the numeric ones. If data is unavailable for a given sequence in a given locale, the display may fall back to ¤ or ¤¤.

No. Replacement Example
¤ Standard currency symbol as in C$12.00
¤¤ ISO currency symbol as in CAD 12.00
¤¤¤ Appropriate currency display name based upon locale and plural rules
¤¤¤¤ Narrow currency symbol as in $12.00

Rule Based Number Formats

CLDR provides an additional mechanism for the formatting of numbers. This approach can be used to format numbers in locale-specific words, or to format numbers in a number system that does not use the decimal digits 0 through 9 such as Chinese and Hebrew.

Formatting numbers as words, ordinals and roman numerals

  • As words. For example, formatting 123 into "one hundred and twenty-three" for the "en" locale. The applicable format types are :spellout and :spellout_verbose.
iex> MyApp.Cldr.Number.to_string 123, format: :spellout
{:ok, "one hundred twenty-three"}

iex> MyApp.Cldr.Number.to_string 123, format: :spellout_verbose
{:ok, "one hundred and twenty-three"}
  • As a year. In many languages the written form of a year is different to that used for an arbitrary number. For example, formatting 1989 would result in "nineteen eighty-nine". The applicable format type is :spellout_year.
iex> MyApp.Cldr.Number.to_string 2017, format: :spellout_year
{:ok, "twenty seventeen"}
  • As an ordinal. For example, formatting 123 into "123rd". The applicable format types are :ordinal, :spellout_ordinal and :spellout_ordinal_verbose.
iex> MyApp.Cldr.Number.to_string 123, format: :ordinal
{:ok, "123rd"}

iex> MyApp.Cldr.Number.to_string 123, format: :spellout_ordinal
{:ok, "one hundred twenty-third"}

iex> MyApp.Cldr.Number.to_string 123, format: :spellout_ordinal_verbose
{:ok, "one hundred and twenty-third"}

iex> MyApp.Cldr.Number.to_string 123, format: :ordinal, locale: "fr"
{:ok, "123e"}

iex> MyApp.Cldr.Number.to_string 123, format: :ordinal, locale: "zh"
{:ok, "第123"}
  • As Roman numerals. For example, formatting 123 into "CXXIII". The applicable formats are :roman or :roman_lower. Note that roman number formatting is only supported for numbers between 1 and 5,000.
iex> MyApp.Cldr.Number.to_string 123, format: :roman
{:ok, "CXXIII"}

iex> MyApp.Cldr.Number.to_string 123, format: :roman_lower
{:ok, "cxxiii"}

iex> MyApp.Cldr.Number.to_string 12345, format: :roman_lower
{:ok, "12,345"}

Converting numbers to non-latin number systems

Some number systems, such as Hebrew and Chinese, do not use the digits 0 through 9 in the their native number system. RBNF defines rules for these and other number systems that can provide number system conversion. MyApp.Cldr.Number.to_string/2 does not support number systems without digits defined therefore another mechanism is required to output numbers in these algorithmic number systems. To support number system conversion, the function Cldr.Number.to_number_system/3 is provided. Note that no formatting is supported, this is a number system conversion only.

For example, to output a number in the :hans numbering system (Chinese) and the Hebrew number system:

iex> Cldr.Number.to_number_system 123, :hans, MyApp.Cldr
{:ok, "一百二十三"}

iex> Cldr.Number.to_number_system 123, :hebr, MyApp.Cldr
{:ok, "ק׳"}

Cldr.Number.to_number_system/3 supports the conversion between numeric number systems (those with digits 0 through 9) in addition to algorithmic number systems (those supported by rules-based number formatting). For example, outputting to the :thai number system:

iex> Cldr.Number.to_number_system 123, :thai, MyApp.Cldr
{:ok, "๑๒๓"}

The known number systems in Cldr can be returned by the function Cldr.Number.System.known_number_systems/0:

iex> Cldr.Number.System.known_number_systems
[:adlm, :ahom, :arab, :arabext, :armn, :armnlow, :bali, :beng, :bhks, :brah,
 :cakm, :cham, :cyrl, :deva, :ethi, :fullwide, :geor, :grek, :greklow, :gujr,
 :guru, :hanidays, :hanidec, :hans, :hansfin, :hant, :hantfin, :hebr, :hmng,
 :java, :jpan, :jpanfin, :kali, :khmr, :knda, :lana, :lanatham, :laoo, :latn,
 :lepc, :limb, :mathbold, :mathdbl, :mathmono, :mathsanb, :mathsans, :mlym,
 :modi, :mong, :mroo, ...]

RBNF rules defined in CLDR

There are also many additional methods more specialised to a specific locale that cater for languages with more complex gender and grammar requirements. Since these rules are specialised to a locale it is not possible to standarise the public API more than described in this section.

The full set of RBNF formats is accessable through the modules MyApp.Cldr.Rbnf.Ordinal, MyApp.Cldr.Rbnf.Spellout and MyApp.Cldr.Rbnf.NumberSystem.

Each of these modules has a set of functions that are generated at compile time that implement the relevant RBNF rules. The available rules for a given locale can be retrieved by calling MyApp.Cldr.Rbnf.Spellout.rule_set(locale) or the same function on the other modules. For example:

iex> MyApp.Cldr.Rbnf.Ordinal.rule_sets "en"
[:digits_ordinal]

iex> MyApp.Cldr.Rbnf.Spellout.rule_sets "fr"
[:spellout_ordinal_masculine_plural, :spellout_ordinal_masculine,
 :spellout_ordinal_feminine_plural, :spellout_ordinal_feminine,
 :spellout_numbering_year, :spellout_numbering, :spellout_cardinal_masculine,
 :spellout_cardinal_feminine]

These rule-based formats are invoked directly on the required module passing the number and locale. For example:

iex> MyApp.Cldr.Rbnf.Spellout.spellout_numbering_year 1989, "fr"
"dix-neuf-cent quatre-vingt-neuf"

iex> MyApp.Cldr.Rbnf.Spellout.spellout_numbering_year 1989, "en"
"nineteen eighty-nine"

iex> MyApp.Cldr.Rbnf.Ordinal.digits_ordinal 1989, "en"
"1,989th"

RBNF Rules with Float numbers

RBNF is primarily oriented towards positive integer numbers. Whilst the standard caters for negative numbers and fractional numbers the implementation of the rules is incomplete. Use with care.