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

[(Ted Harding)]

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.

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Date: 06-Jun-08                                       Time: 02:18:00
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