[R] round function seems to produce maximum 2 decimals

[(Ted Harding)]

On 20-May-09 20:10:15, Glenn E Stauffer wrote:
> I am trying to use round()to force R to display a specific number
> of decimals, but it seems to display <=2 decimals no matter what I
> specify in the digits argument. As an alternative I tried signif(),
> but it also produces unexpected results. See example code and results
> below.
> Format() works, but then the result no longer is numeric. Am I missing
> something simple?
> I am using R 2.9.0 on Windows XP. 
> Thanks,
> Glenn
> 
>#code
> h=12345.16711
> h
> 
> round(h,digits=1)
> round(h,digits=2)
> round(h,digits=3)
> round(h,digits=4)
> round(h,digits=5)
> 
> signif(h,digits=9)
> 
> format(h,nsmall=4)
> 
>#results
>> h=12345.16711
>> h
> [1] 12345.17
>> round(h,digits=1)
> [1] 12345.2
>> round(h,digits=2)
> [1] 12345.17
>> round(h,digits=3)
> [1] 12345.17
>> round(h,digits=4)
> [1] 12345.17
>> round(h,digits=5)
> [1] 12345.17
>> signif(h,digits=9)
> [1] 12345.17
>> 
>> format(h,nsmall=4)
> [1] "12345.1671"

What you're missing is that when you do (e.g.)

  h <- 12345.16711
  round(h,digits=4)
# [1] 12345.17

what is displayed ("[1] 12345.17") is not the result of round(),
but what the result of round() is to be displayed as given the
options digits=7 (default) for the number of *significant figures*
in the display of stored values.

To see the result as it is stored, you should use print() with
the appropriate number of disgits specified:

  print( round(h,digits=5),10)
# [1] 12345.16711
  print( round(h,digits=4),10)
# [1] 12345.1671
  print( round(h,digits=3),10)
# [1] 12345.167
  print( round(h,digits=2),10)
# [1] 12345.17

Internally, round(h) is correctly stored:

  h4 <- round(h,4)
  h - h4
# [1] 1e-05
  h3 <- round(h,3)
  h - h3
# [1] 0.00011
  h2 <- round(h,2)
  h - h2
# [1] -0.00289

To illustrate the influence of the display option digits=7:

  h<-45.16711
  h
# [1] 45.16711
  round(h,digits=4)
# [1] 45.1671
   round(h,digits=3)
# [1] 45.167
  round(h,digits=2)
# [1] 45.17

  h<-345.16711
  h
# [1] 345.1671
   round(h,digits=4)
# [1] 345.1671
   round(h,digits=3)
# [1] 345.167
   round(h,digits=2)
# [1] 345.17

  h<-2345.16711
  h
# [1] 2345.167
  round(h,digits=4)
# [1] 2345.167
   round(h,digits=3)
# [1] 2345.167
  round(h,digits=2)
# [1] 2345.17

Hoping this helps,
Ted.

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E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 20-May-09                                       Time: 22:54:41
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