function truncate (s_trunc)
s_trunc = string.gsub(s_trunc, ",", "")
n_trunc = tonumber(s_trunc)
if (string.len(s_trunc) >= 1) and (string.len(s_trunc) <= 3) then
return s_trunc
elseif (string.len(s_trunc) >= 4) and (string.len(s_trunc) <= 6) then
n_divide = 1000
n_class = "thousand"
elseif (string.len(s_trunc) >= 7) and (string.len(s_trunc) <= 9) then
n_divide = 1000000
n_class = "million"
elseif (string.len(s_trunc) >= 10) and (string.len(s_trunc) <= 12) then
n_divide = 1000000000
n_class = "billion"
elseif (string.len(s_trunc) >= 13) and (string.len(s_trunc) <= 15) then
n_divide = 1000000000000
n_class = "trillion"
elseif (string.len(s_trunc) >= 16) and (string.len(s_trunc) <= 18) then
n_divide = 1000000000000000
n_class = "quadrillion"
elseif (string.len(s_trunc) >= 19) and (string.len(s_trunc) <= 21) then
n_divide = 1000000000000000000
n_class = "quintillion"
elseif (string.len(s_trunc) >= 22) and (string.len(s_trunc) <= 24) then
n_divide = 1000000000000000000000
n_class = "sextillion"
elseif (string.len(s_trunc) >= 25) and (string.len(s_trunc) <= 27) then
n_divide = 1000000000000000000000000
n_class = "septillion"
elseif (string.len(s_trunc) >= 28) and (string.len(s_trunc) <= 30) then
n_divide = 1000000000000000000000000000
n_class = "octillion"
else
return "error"
end
return string.gsub(string.format("%.1f", n_trunc/n_divide), "%.0", "").." "..n_class
end

function truncate (str)
  str = string.gsub(str, ",", "")  -- get rid of commas
  len = string.len (string.match (str, "%d+"))  -- find size of integer portion
  if (len >= 1) and (len <= 3) then
    return str
  elseif (len >= 4) and (len <= 6) then
    divideBy = 1E3
    numberSize = "thousand"
  elseif (len >= 7) and (len <= 9) then
    divideBy = 1E6
    numberSize = "million"
  elseif (len >= 10) and (len <= 12) then
    divideBy = 1E9
    numberSize = "billion"
  elseif (len >= 13) and (len <= 15) then
    divideBy = 1E12
    numberSize = "trillion"
  elseif (len >= 16) and (len <= 18) then
    divideBy = 1E15
    numberSize = "quadrillion"
  elseif (len >= 19) and (len <= 21) then
    divideBy = 1E18
    numberSize = "quintillion"
  elseif (len >= 22) and (len <= 24) then
    divideBy = 1E21
    numberSize = "sextillion"
  elseif (len >= 25) and (len <= 27) then
    divideBy = 1E24
    numberSize = "septillion"
  elseif (len >= 28) and (len <= 30) then
    divideBy = 1E27
    numberSize = "octillion"
  else
    return "number error: " .. str
  end
  -- divide down, convert to float, omit trailing ".0", show one decimal place
  return string.gsub(string.format("%.1f", tonumber(str)/divideBy), "%.0", "") .. " " .. numberSize
end


print (truncate ("8,600,000,000.22"))
print (truncate ("1234.567"))
print (truncate ("123.456"))
print (truncate ("8,000,000,000."))

8.6 billion
1.2 thousand
123.456
8 billion

  return string.gsub(string.format("%.1f", tonumber(str)/divideBy - 0.05), "%.0", "") .. " " .. numberSize