Formatting Numbers

wiki

Alternative code further down.

-- from sam_lie

-- Compatible with Lua 5.0 and 5.1.

-- Disclaimer : use at own risk especially for hedge fund reports :-)



---============================================================

-- add comma to separate thousands

-- 

function comma_value(amount)

  local formatted = amount

  while true do  

    formatted, k = string.gsub(formatted, "^(-?%d+)(%d%d%d)", '%1,%2')

    if (k==0) then

      break

    end

  end

  return formatted

end



---============================================================

-- rounds a number to the nearest decimal places

--

function round(val, decimal)

  if (decimal) then

    return math.floor( (val * 10^decimal) + 0.5) / (10^decimal)

  else

    return math.floor(val+0.5)

  end

end



--===================================================================

-- given a numeric value formats output with comma to separate thousands

-- and rounded to given decimal places

--

--

function format_num(amount, decimal, prefix, neg_prefix)

  local str_amount,  formatted, famount, remain



  decimal = decimal or 2  -- default 2 decimal places

  neg_prefix = neg_prefix or "-" -- default negative sign



  famount = math.abs(round(amount,decimal))

  famount = math.floor(famount)



  remain = round(math.abs(amount) - famount, decimal)



        -- comma to separate the thousands

  formatted = comma_value(famount)



        -- attach the decimal portion

  if (decimal > 0) then

    remain = string.sub(tostring(remain),3)

    formatted = formatted .. "." .. remain ..

                string.rep("0", decimal - string.len(remain))

  end



        -- attach prefix string e.g '$' 

  formatted = (prefix or "") .. formatted 



        -- if value is negative then format accordingly

  if (amount<0) then

    if (neg_prefix=="()") then

      formatted = "("..formatted ..")"

    else

      formatted = neg_prefix .. formatted 

    end

  end



  return formatted

end

Example usage:

amount = 1333444.1

print(format_num(amount,2))

print(format_num(amount,-2,"US$"))



amount = -22333444.5634

print(format_num(amount,2,"$"))

print(format_num(amount,2,"$","()"))

print(format_num(amount,3,"$","NEG "))

Output:

1,333,444.10

US$1,333,400

-$22,333,444.56

($22,333,444.56)

NEG $22,333,444.563

RichardWarburton alternate version:

function comma_value(n) -- credit http://richard.warburton.it

	local left,num,right = string.match(n,'^([^%d]*%d)(%d*)(.-)$')

	return left..(num:reverse():gsub('(%d%d%d)','%1,'):reverse())..right

end

Example usage:

print(comma_value(9))

print(comma_value(999))

print(comma_value(1000))

print(comma_value('1333444.10'))

print(comma_value('US$1333400'))

print(comma_value('-$22333444.56'))

print(comma_value('($22333444.56)'))

print(comma_value('NEG $22333444.563'))

Output:

9

999

1,000

1,333,444.10

US$1,333,400

-$22,333,444.56

($22,333,444.56)

NEG $22,333,444.563