comment on

I have yet to find a display format for arbitrary floating point numbers that I like much. I wanted something closer to "Engineering notation" (exponents are always a multiple of 3) but this works for now.

Number always take up 9 characters
Perl doesn't handle any numbers too large or too small to fit (you'd have to go smaller than 1.0e-999 or larger than 9.99e999)
Numbers of similar magnitude line up their decimal points

The code is tested but could probably be improved a great deal.

I'd like to be able to make the width a parameter (instead of fixed at 9). Being able to go as low as 7 (or even 6) would be way cool.

#!/usr/bin/perl -w
use strict;

Main();
exit( 0 );

{

    my( %fmt4exp, @exps2fmt, $fullfmt );

    BEGIN {
        %fmt4exp= (
            -100 => '+1.0e-999',
             -10 => '+1.00e-99',
              -5 => '+1.000e-9',
              -1 => '+0.000000',
              +3 => '   +0.000',
              +5 => '     +0.0',
              +7 => '       +0',
              +9 => '+1.000e+9',
             +99 => '+1.000e99',
          +99999 => '+1.00e999',
        );
        @exps2fmt= sort {$a<=>$b} keys %fmt4exp;
        $fullfmt= '%+14.7e'; # %+1.2345678e-99
    }

    sub Num2Str {
        my( $num )= @_;
        my $full= sprintf $fullfmt, $num;
        my( $sign, $one, $rest, $esign, $eabs )=
            $full =~ m<
                ^\s*
                ([-+]?)(\d)\.(\d*)
                [eE]([-+]?)(\d+)
                \s*$
            >x;
        my $exp= $esign . $eabs;
        my $fmt;
        for my $exp2fmt (  @exps2fmt  ) {
            if(  $exp <= $exp2fmt  ) {
                $fmt= $fmt4exp{$exp2fmt};
                last;
            }
        }
        my $str= $fmt;
        if(  $fmt =~ /e/  ) {
            $str =~ s/\+/$sign/;
            $str =~ s/1/$one/;
            $str =~ s{\.(0+)(?=[eE])}{
                (   sprintf( "%14.".length($1)."e", $num )
                        =~ /(\.\d+)/
                )[0]
            }e;
            $str =~ s/(9+)/sprintf "%0".length($1)."d", $eabs/e;
        } else {
            if(  $exp < 0  ) {
                $str =~ s/\+/$sign/;
                $rest= '0'x($eabs-1) . $one . $rest;
            } else {
                $one= substr( $one . $rest, 0, 1+$exp );
                substr( $rest, 0, $exp )= '';
                $str =~ s/([\s+0]+)/sprintf "%+".length($1)."s", $sign
+.$one/e;
            }
            $str =~ s{\.(0+)}{
                (   sprintf( "%14.".length($1)."f", $num )
                        =~ /(\.\d+)$/
                )[0]
            }e;
            $str =~ s{\.(0+)$}{
                (   sprintf( "%14.".length($1)."f", $num )
                        =~ /(\.\d+)/
                )[0]
            }e;
            $str =~ s/(\.?0+)$/' ' x length($1)/e
                if  $fmt =~ /\./;
        }
        return $str;
    }

}

sub Main {
    for my $exp (  -101..-98, -11, -10..11, 98..101  ) {
        for my $sign (  '', '-'  ) {
            my $num= 0 + ( $sign . "5.555555555e" . $exp );
            printf "%-20s (%s)\n", $num, Num2Str($num);
        }
    }
    for my $exp (  -10..11 ) {
        for my $sign (  '', '-'  ) {
            my $num= 0 + ( $sign . "1e" . $exp );
            printf "%-20s (%s)\n", $num, Num2Str($num);
            printf "%-20s (%s)\n", 0, Num2Str(0)
                if  1 == $num;
        }
    }
}
[download]

In reply to Display floating point numbers in compact, fixed-width format by tye

Are you posting in the right place? Check out Where do I post X? to know for sure.
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
Want more info? How to link or How to display code and escape characters are good places to start.


laziness, impatience, and hubris
	PerlMonks