How do I improve regex to eliminate unnecessary method chaining?

问题

This functional method takes a number and returns the same value separated with commas, as is the common convention in the US.

The only way I could get it to work with regex was to reverse the string before and after the expression. Is there a regex that can help me eliminate the need to call String#reverse twice for method functionality?

def separate_comma(number)
  raise "You must enter a number." if number.is_a?(Numeric) == false
  number.to_s.reverse.gsub(/(\d{3})(?=\d{1,3})/, "\\1,").reverse
end

回答1:

"1234556".gsub(/\d(?=\d{3}+\b)/,'\\0,')
# => "1,234,556"

This doesn't handle long fractional values, but this wasn't a concern for the OP's regex either.

回答2:

Other libraries have already solved this problem - ActiveSupport for one.

require "active_support/number_helper"
ActiveSupport::NumberHelper.number_to_delimited(1234567890)
#=> "1,234,567,890"

You can even change the delimiter if you wish:

ActiveSupport::NumberHelper.number_to_delimited(1234567890, delimiter: "|")
#=> "1|234|567|890"

回答3:

The established way to do it is:

string.gsub(/(?<=\d)(?=(?:\d{3})+\z)/, ",")

If you want to do it with floats:

string.gsub(/(?<=\d)(?=(?:\d{3})+[.\z])/, ",")

来源：https://stackoverflow.com/questions/21892046/how-do-i-improve-regex-to-eliminate-unnecessary-method-chaining