Re: [R] Why doesn't formatC( x, digits=2, format="g") doesn't al

From: Ted Harding <Ted.Harding_at_manchester.ac.uk>
Date: Fri, 06 Jun 2008 02:18:03 +0100 (BST)


On 06-Jun-08 00:48:50, Peter Dunn wrote:
> Hi all
> I am not a C programmer, but I am trying to understand formatC to
> get consistent printing of reals to a given number of significant
> digits.
> Can someone please explain this to me? These first three give what
> I expect on reading ?formatC:
>

>> formatC(0.0059999, digits=2,format="fg",flag="#")

> [1] "0.0060"
>> formatC(0.59999, digits=2,format="fg",flag="#")

> [1] "0.60"
>> formatC(5.9999, digits=2,format="fg",flag="#")

> [1] "6.0"
>
> This seems consistent with what I read (but perhaps do not
> understand) in ?formatC, where I read this:
>
> digits the desired number of digits after the decimal point
> (format = "f") or significant digits (format = "g", = "e" or
> = "fg").
>
> Since I am using format="fg" and digits=2, so I am expecting two
> significant digits to always show, which I have above. So I fail to
> understand this:
>
>> formatC(0.000059999, digits=2,format="fg",flag="#")

> [1] "0.00006"
>> formatC(0.000059, digits=2, format="fg",flag="#")

> [1] "0.000059"
>
> I was expecting both of these to produce "0.000059". But in the
> first case above, I get one significant digit only.
>
> I'm obviously misunderstanding something; can someone enlighten me?
> (No doubt, someone will point out a nuance of the help files I
> didn't understand!)

I think that what is happening is that 0.000059999 rounds (to 2 significant digits) to 0.000060 in the first instance, and the "0", not being "significant" (it adds no information to 0.00006), is dropped.

> Also, since the above obviously doesn't do what I hoped
> (consistently printing two sig figs), could someone also explain
> how I can consistently get two significant figures in situation
> like above?

I don't know! I thought using the "width" parameter might do it, but it does not affect the number of decimal places printed.

> Thanks as always.
> P.

Sorry I coujldn't be more helpful!
Ted.



E-Mail: (Ted Harding) <Ted.Harding_at_manchester.ac.uk> Fax-to-email: +44 (0)870 094 0861
Date: 06-Jun-08                                       Time: 02:18:00
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