From: Rob Biedenharn <Rob@...>
Date: 2009-05-16T02:45:59+09:00
Subject: Re: Rounding any number (int or float) to 3 significant figures


On May 15, 2009, at 12:57 PM, Max Williams wrote:

> I have a requirement where i need to display (ie convert to a string)
> all digits to 3 significant figures.  (not the same as 3 decimal  
> places)
>
> eg
>
>    23 => "23"
>    26759 => "26,800"
>    10.546 => "10.5"
>    3332332 => "3,330,000"
>    0.766 => "0.766"
>    0.00000766 => "0.00000766"
>
> Can anyone show me a neat way to do this?  I'd have thought that  
> there'd
> be a method for it already but i can't find one.
>
> thanks!
> max
> -- 

This should get you started:

irb> h.each do |n,s|
irb>   puts( ("%f"%[("%.3g"%n).to_f]).sub(/\.?0*\z/,'') )
irb> end
0.766
23
26800
10.5
3330000
0.000008
=> {0.766=>"0.766", 23=>"23", 26759=>"26,800", 10.546=>"10.5",  
3332332=>"3,330,000", 7.66e-06=>"0.00000766"}

It doesn't do so well with the smallest value, but if you know the  
ranges you're dealing with, perhaps you can adjust the %f spec.

-Rob

Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com