Fractional component of a number

Dear all,
I am happy to accept that

is.integer(1)

[1] FALSE

But I'm having difficulty with this one:

as.integer((2.53-2)*100)

[1] 52

especially since:

as.integer((1.53-1)*100)

[1] 53

Although I know that this is a precision issue since

x <- (2.53-2)*100
x-53

[1] -2.131628e-14

And I can always use the round function to get what I want,
but I just wonder if something is wrong here.

sessionInfo()

R version 2.13.1 (2011-07-08)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=Thai_Thailand.874  LC_CTYPE=Thai_Thailand.874   
LC_MONETARY=Thai_Thailand.874
[4] LC_NUMERIC=C                  LC_TIME=Thai_Thailand.874

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

Thanks,
Edward

It depends on what you mean by "wrong"! Perhaps "unexpected"
might be better!

The key to the matter is described in '?as.integer' under "Value":

  Non-integral numeric values are truncated towards zero
  (i.e., ?as.integer(x)? equals ?trunc(x)? there) ...

so that

  as.integer(2)
  # [1] 2
  as.integer(2 + 2e-14)
  # [1] 2
  as.integer(2 - 2e-14)
  # [1] 1
  as.integer(-2 + 2e-14)
  # [1] -1
  as.integer(-2 - 2e-14)
  # [1] -2


so it is doing "what it says on the box". Yes, you are better
using round()!

Hoping this helps to clear it up,
Ted.

--------------------------------------------------------------------
E-Mail: (Ted Harding) <ted.harding at wlandres.net>
Fax-to-email: +44 (0)870 094 0861
Date: 28-Aug-11                                       Time: 09:24:14
------------------------------ XFMail ------------------------------