Mirror of forum.nim-lang.org

13606 :: significant figures library for nim?

• sonicsmooth (orginal) [2026-01-01T08:07:01+01:00] view original

  I looked but was unable to find anything similar to Python's sigfig library. Does something like this exist for Nim?

  I want to be able to express a number with a given amount of significant digits. Ideally I'd have the option to show this in scientific or engineering notation too.

  I tried getting Grok AI to give me a start, but it kept trying to do nested curly braces in the fmt call.

  thanks

---

• janAkali (orginal) [2026-01-01T09:11:13+01:00] view original

  If you only need a string value for output, use strutils.formatfloat():

  
  import std/strutils
  echo formatFloat(123.129, ffDecimal, 2)    # 123.13
  echo formatFloat(123.129, ffScientific, 2) # 1.23e+02
  Run

  If you need actual fp number rounded by decimals - I don't see the point, but here is how you can do this:

  
  import std/math
  
  proc truncToDecimal[T: SomeFloat](n: T, places: Natural): T =
    let t = T(10 ^ places)
    trunc(n * t) / t
  
  proc roundToDecimal[T: SomeFloat](n: T, places: Natural): T =
    let t = T(10 ^ places)
    round(n * t) / t
  
  echo roundToDecimal(123.1299999, 2) # 123.13
  
  echo truncToDecimal(123.1299999, 0) # 123.0
  echo truncToDecimal(123.1299999, 1) # 123.1
  echo truncToDecimal(123.1299999, 2) # 123.12
  echo truncToDecimal(123.1299999, 3) # 123.129
  Run

---