Regex to Match Numbers in Plain English
This page presents a regular expression to match numbers in plain English, such as:
one trillion seven hundred twenty two zero point nine five nine hundred ninety nine thousand two hundred thirteen
This pattern was an excuse to build a beautiful regex using the defined subroutine syntax (?(DEFINE) … ). As such, it only works in engine that support that syntax—currently Perl, PCRE (PHP, Delphi, R…) and Python's alternate regex engine.
The regex built in a modular way—like lego. We define some named subroutines—one_to_9, ten_to_19—then more named subroutines that build on the earlier ones: one_to_99, one_to_999…
At the bottom, after defining all the groups, is where the real matching begins. There you can decide to match a big number by calling the big_number subroutine with (?&bignumber), or to match smaller numbers using subroutines such as (?&one_to_99), and so on.
There are plenty of comments in the regex, so if you read the defined subroutine page, you shouldn't need further explanations.
(direct link)
(?x) # free-spacing mode
(?(DEFINE)
# Within this DEFINE block, we'll define many subroutines
# They build on each other like lego until we can define
# a "big number"
(?<one_to_9>
# The basic regex:
# one|two|three|four|five|six|seven|eight|nine
# We'll use an optimized version:
# Option 1: four|eight|(?:fiv|(?:ni|o)n)e|t(?:wo|hree)|
# s(?:ix|even)
# Option 2:
(?:f(?:ive|our)|s(?:even|ix)|t(?:hree|wo)|(?:ni|o)ne|eight)
) # end one_to_9 definition
(?<ten_to_19>
# The basic regex:
# ten|eleven|twelve|thirteen|fourteen|fifteen|sixteen|seventeen|
# eighteen|nineteen
# We'll use an optimized version:
# Option 1: twelve|(?:(?:elev|t)e|(?:fif|eigh|nine|(?:thi|fou)r|
# s(?:ix|even))tee)n
# Option 2:
(?:(?:(?:s(?:even|ix)|f(?:our|if)|nine)te|e(?:ighte|lev))en|
t(?:(?:hirte)?en|welve))
) # end ten_to_19 definition
(?<two_digit_prefix>
# The basic regex:
# twenty|thirty|forty|fifty|sixty|seventy|eighty|ninety
# We'll use an optimized version:
# Option 1: (?:fif|six|eigh|nine|(?:tw|sev)en|(?:thi|fo)r)ty
# Option 2:
(?:s(?:even|ix)|t(?:hir|wen)|f(?:if|or)|eigh|nine)ty
) # end two_digit_prefix definition
(?<one_to_99>
(?&two_digit_prefix)(?:[- ](?&one_to_9))?|(?&ten_to_19)|
(?&one_to_9)
) # end one_to_99 definition
(?<one_to_999>
(?&one_to_9)[ ]hundred(?:[ ](?:and[ ])?(?&one_to_99))?|
(?&one_to_99)
) # end one_to_999 definition
(?<one_to_999_999>
(?&one_to_999)[ ]thousand(?:[ ](?&one_to_999))?|
(?&one_to_999)
) # end one_to_999_999 definition
(?<one_to_999_999_999>
(?&one_to_999)[ ]million(?:[ ](?&one_to_999_999))?|
(?&one_to_999_999)
) # end one_to_999_999_999 definition
(?<one_to_999_999_999_999>
(?&one_to_999)[ ]billion(?:[ ](?&one_to_999_999_999))?|
(?&one_to_999_999_999)
) # end one_to_999_999_999_999 definition
(?<one_to_999_999_999_999_999>
(?&one_to_999)[ ]trillion(?:[ ](?&one_to_999_999_999_999))?|
(?&one_to_999_999_999_999)
) # end one_to_999_999_999_999_999 definition
(?<bignumber>
zero|(?&one_to_999_999_999_999_999)
) # end bignumber definition
(?<zero_to_9>
(?&one_to_9)|zero
) # end zero to 9 definition
(?<decimals>
point(?:[ ](?&zero_to_9))+
) # end decimals definition
) # End DEFINE
####### The Regex Matching Starts Here ########
(?&bignumber)(?:[ ](?&decimals))?
### Other examples of groups we could match ###
#(?&bignumber)
# (?&one_to_99)
# (?&one_to_999)
# (?&one_to_999_999)
# (?&one_to_999_999_999)
# (?&one_to_999_999_999_999)
# (?&one_to_999_999_999_999_999)
You can play with the regex and sample text in this live regex demo.
