R help - Mar 2009 - "digits" in round()

Hi Folks,

Compare

  print(1234567890,digits=4)
# [1] 1.235e+09
  print(1234567890,digits=5)
# [1] 1234567890

Granted that

  digits: a non-null value for 'digits' specifies the minimum
          number of significant digits to be printed in values.

how does R decide to switch from the "1.235e+09" (rounded to
4 digits, i.e. the minumum, in "e" notation) to "1234567890"
(the
complete raw notation, 10 digits) when 'digits' goes from 4 to 5?

Thanks,
Ted.

--------------------------------------------------------------------
E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 31-Mar-09                                       Time: 13:59:37
------------------------------ XFMail ------------------------------

On 3/31/2009 8:59 AM, (Ted Harding) wrote:
> Hi Folks,
> 
> Compare
> 
>   print(1234567890,digits=4)
> # [1] 1.235e+09
>   print(1234567890,digits=5)
> # [1] 1234567890
If printing in scientific notation takes up as much space or more than 
printing in regular notation, then regular notation will be used.

In this case the 5 digit scientific notation output of 1.2346e+09 takes 
10 characters, so the 10 character simple format is used instead.

The reason for this rule is that regular notation gives more information 
about the number.  If you had wanted to use 10 chars but be less 
expressive you would have used an explicit format.

Duncan Murdoch
> Granted that
> 
>   digits: a non-null value for 'digits' specifies the minimum
>           number of significant digits to be printed in values.
> 
> how does R decide to switch from the "1.235e+09" (rounded to
> 4 digits, i.e. the minumum, in "e" notation) to
"1234567890" (the
> complete raw notation, 10 digits) when 'digits' goes from 4 to 5?
> 
> Thanks,
> Ted.
> 
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
> Fax-to-email: +44 (0)870 094 0861
> Date: 31-Mar-09                                       Time: 13:59:37
> ------------------------------ XFMail ------------------------------
> 
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>>>>> "TH" == Ted Harding <Ted.Harding at
manchester.ac.uk>
>>>>>     on Tue, 31 Mar 2009 13:59:41 +0100 (BST) writes:
    TH> Hi Folks,
    TH> Compare

    TH> print(1234567890,digits=4)
    TH> # [1] 1.235e+09
    TH> print(1234567890,digits=5)
    TH> # [1] 1234567890

    TH> Granted that

    TH> digits: a non-null value for 'digits' specifies the minimum
    TH> number of significant digits to be printed in values.

    TH> how does R decide to switch from the "1.235e+09" (rounded
to
    TH> 4 digits, i.e. the minumum, in "e" notation) to
"1234567890" (the
    TH> complete raw notation, 10 digits) when 'digits' goes from 4
to 5?

that's easy (well, as I'm one of the co-implementors ...) :

One of the design ideas has been to use "e"-notation only when
it's shorter (under the constraints given by 'digits'), i.e.,

   1.2346e+09
is not shorter (but has less information) than
   1234567890
hence the latter is chosen.
There are quite a few cases, and constraints (*) that apply
simultaneously, such that sometimes the default numeric
formatting may seem peculiar,  but I hope that in the mean
time  we have squished all real bugs here.

*) such as platform (in)dependency; S - back-compatibility, ..

Best regards,
Martin Maechler, ETH Zurich