I'm don't fully understand the 'f' and 'g' options in the format function. What are they doing here:
"11234.2"
> (format {%f} 11234.17)
"11234.170000"
>
How does one get format to print exactly what it's given (in this case), without trailing zeros?
The "%g" format chooses either the "%f" or the "%e" format depending on the size/precision of the number:
"134.178"
> (format {%g} 134.1789)
"134.179"
> (format {%g} 12345.6)
"12345.6"
> (format {%g} 12345.67)
"12345.7"
> (format {%g} 123456.7)
"123457"
> (format {%g} 1234567)
"1.23457e+06"
>
The number gets rounded to 6 digits precicion, and if there are more than 6 before the decimal point then"%g" switches to the "%e" format.
You can force this rounding effect to certain precision by specifiying field width and precision in the "%w.pg" format:
> (format {%8.4g} 12.34)
" 12.34"
> (format {%8.4g} 12.345)
" 12.35"
> (format {%8.4g} 12345)
"1.234e+04"
> (format {%8.4g} 1234)
" 1234"
>
The format coding used in newLISP comes from the C-language and is used by most programming languages today, i.e. Perl, Python and Ruby.
Lutz
Thanks. I'll avoid %g...;-) But how do I get a number printed out without rounding but without added zeros:
;-> "11234.170000"
ie I want as many digits as there are, but no more... I suppose I could trim the zeroes off...
"11234.17"
but then:
"11234."
How about another approach?
"11234.17"
> (string 11234.0)
"11234"
> (string 11234)
"11234"
Good idea - it certainly works in many cases! My education is still in progress about number precision... ;-) but Lutz says (//http://newlisp-on-noodles.org/wiki/index.php/Talk:Quiz_3:_Fractran)
Quote
string will cut off all digits after the 10th decimal digit
so it should be used carefully...
Using 'string' is like using the "%1.10g" format and will limit the number to 10 digits precision.
- The 'g' format will automatically cut of trailing zero's.
- the 10 tells it to do maximum 10 digits precicion overall before and after the decimal point.
- the 1 for the width field forces it to use the least amount of space possible. If you would specify "%20.10g" the printout would be in a 20 spaces wide field.
To sum it up: Use the %w.pg" format it gives you the most control and cuts of trailing 0's
"12345.67"
> (format "%1.10g" 1234567.670000)
"1234567.67"
> (format "%1.10g" 123456789.670000)
"123456789.7"
> (format "%20.10g" 123456789.670000)
" 123456789.7"
>
The last example shows the 'w' field with 20 right-aligning the number into it. I also shows the 10th digit rounded, because the maximum precision specified is reached by the number.
Lutz
.. and I forgot the maximum precision for the p in "%w.pg" would be 15.
Lutz
This is good, thanks. One day it might go into the manual, perhaps...!
cheers Lutz
The current description of 'format' in the newLISP manual is terse. There is a good summary of the functioning of all formatting characters in:
http://en.wikipedia.org/wiki/Printf
On the page scroll down to the heading: "printf format placeholders"
Note that some features are omitted in newLISP. Similar to regular expression syntax, C-language like formatting is today one of the few features emerging as standards in all programming languages.
Lutz