R help - Jun 2003 - Rounding problem R vs Excel

For numbers ending in 5 Excel always rounds up and I want to reproduce this in R
rather than use the round function.
I have tried:

x<-as.integer(x*100+0.5)/100

and

x<-floor(x*100+0.5)/100

However, some values of x cause problems e.g

x<-floor(4.145*100+0.5)/100
4.14

I have tried breaking it down into steps and force the results to 10 significant
figures in the following function, which seems to work

roundoff<-function(x){
a<-signif(x*100+0.5,digits=10)
roundoff<-floor(a)/100
roundoff
}

Is there a more sensible way of do this for all numbers?

Thanks
Mike

	[[alternate HTML version deleted]]

Does this script do what you want?

cround <- function(x,digits=0) {
   a <- ifelse(x>0,.5,-.5)
   if (digits==0) {
     floor(x+a)
   } else {
     m <- 10^digits
     floor(x*m+a)/m
   }
}

 > cround(1.4535,1)
[1] 1.5
 > cround(1.4535,2)
[1] 1.45
 > cround(1.4535,3)
[1] 1.454
 > cround(1.4535,4)
[1] 1.4535


   - Hedderik.

I don't have the reference, but a biologist friend of mine
once showed me a refereed journal article that purported
to demonstrate numerical errors made by MSExcel.  This 
would have been Excel97 or Excel2000... In any case, the
journal's scope was biological in nature and the article 
was of interest since Excel is heavily used in that community.

-david paul

-----Original Message-----
From: Duncan Murdoch [mailto:dmurdoch at pair.com] 
Sent: Wednesday, June 04, 2003 8:34 AM
To: MSchwartz at medanalytics.com
Cc: R-help at stat.math.ethz.ch
Subject: Re: [R] Rounding problem R vs Excel


On 04 Jun 2003 00:24:08 -0500, you wrote:
>Excel 2002 (XP):
>
>Cell Formula          Value
>= 0.5 - 0.4 - 0.1     0.00000000000000000000E+00
>=(0.5 - 0.4 - 0.1)    -2.77555756156289000000E-17
 ...
>What is interesting is the change in the displayed value in Excel when 
>the second formula is surrounded by parens (which I found purely by 
>accident). This would suggest that there may be something going on in 
>the parsing of the cell formula that affects the calculation and 
>displayed value.
"Interesting"?  I'd say "horrifying".  When (expr) does
not evaluate the
same as expr, what can you trust?

Duncan Murdoch

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