[R] "digits" doesn't work in format function

[Marc Schwartz]

On Thu, 2007-03-22 at 09:59 -0500, Baoqiang Cao wrote:
> Dear All,
> 
> I was trying to format a numeric vector (100*1) by using
> outd <- format(x=m, sci=F, digits=2)
> 
> > outd[1:10]
>  [1] " 0.01787758" "-0.14760306" "-0.45806041" "-0.67858525" "-0.64591748"
>  [6] "-0.05918100" "-0.25632276" "-0.15980138" "-0.08359873" "-0.37866688"
> >m[1:10]
>  [1]  0.017878 -0.147603 -0.458060 -0.678585 -0.645917 -0.059181 -0.256323
>  [8] -0.159801 -0.083599 -0.378667
> 
> I'm expecting something like, 0.02 -0.15 ...
> 
> Any advice how to fix it will be highly appreciated!
> 
> Best,
>  Baoqiang

The digits argument pertains to the number of _significant digits_. 

>From ?format:

how many significant digits are to be used for numeric and complex x.
The default, NULL, uses getOption(digits). This is a suggestion: enough
decimal places will be used so that the smallest (in magnitude) number
has this many significant digits, and also to satisfy nsmall. (For the
interpretation for complex numbers see signif.)


If you want tight and consistent control over the number of digits after
the decimal place, you would need to use ?sprintf or ?formatC:

> sprintf("%.2f", m)
 [1] "0.02"  "-0.15" "-0.46" "-0.68" "-0.65" "-0.06" "-0.26" "-0.16"
 [9] "-0.08" "-0.38"


> formatC(m, format = "f", digits = 2)
 [1] "0.02"  "-0.15" "-0.46" "-0.68" "-0.65" "-0.06" "-0.26" "-0.16"
 [9] "-0.08" "-0.38"


HTH,

Marc Schwartz