Contribution: nice floating point number formatting

[Al Christians]

One other option that is often(?) used when numbers are embedded in 
text is to include  the thousands separator only when the number is 
10,000 or more.  The eye doesn't need the comma to read four digits.
So we would write 1234.56 and 12,345.67.  This doesn't work for numbers 
arranged in columns. 


Al
   

"David S. Harrison" wrote:
> 
> Having written a bunch of scientific software, I am always amazed
> at how few languages have built in routines for displaying numbers
> nicely.  I was doing a little programming in Python and got surprised
> again.  I couldn't find any routines for displaying numbers to
> a significant number of digits and adding appropriate commas and
> spaces to long digit sequences.  Below is my attempt to write
> a nice number formatting routine for Python.  It is not particularly
> fast.  I suspect building the string by concatenation is responsible
> for much of its slowness.  Suggestions on how to improve the
> implementation will be gladly accepted.
> 
>                         David S. Harrison
>                         (daha at best.com)
> 
> # ---------------------- cut here --------------------------
> import math
> 
> # Returns a nicely formatted string for the floating point number
> # provided.  This number will be rounded to the supplied accuracy
> # and commas and spaces will be added.  I think every language should
> # do this for numbers.  Why don't they?  Here are some examples:
> # >>> print niceNum(123567.0, 1000)
> # 124,000
> # >>> print niceNum(5.3918e-07, 1e-10)
> # 0.000 000 539 2
> # This kind of thing is wonderful for producing tables for
> # human consumption.
> #
> def niceNum(num, precision):
>     """Returns a string representation for a floating point number
>     that is rounded to the given precision and displayed with
>     commas and spaces."""
>     accpow = math.floor(math.log10(precision))
>     if num < 0:
>         digits = int(math.fabs(num/pow(10,accpow)-0.5))
>     else:
>         digits = int(math.fabs(num/pow(10,accpow)+0.5))
>     result = ''
>     if digits > 0:
>         for i in range(0,accpow):
>             if (i % 3)==0 and i>0:
>                 result = '0,' + result
>             else:
>                 result = '0' + result
>         curpow = int(accpow)
>         while digits > 0:
>             adigit = chr((digits % 10) + ord('0'))
>             if (curpow % 3)==0 and curpow!=0 and len(result)>0:
>                 if curpow < 0:
>                     result = adigit + ' ' + result
>                 else:
>                     result = adigit + ',' + result
>             elif curpow==0 and len(result)>0:
>                 result = adigit + '.' + result
>             else:
>                 result = adigit + result
>             digits = digits/10
>             curpow = curpow + 1
>         for i in range(curpow,0):
>             if (i % 3)==0 and i!=0:
>                 result = '0 ' + result
>             else:
>                 result = '0' + result
>         if curpow <= 0:
>             result = "0." + result
>         if num < 0:
>             result = '-' + result
>     else:
>         result = "0"
>     return result