On 07/01/2010 7:31 AM, Ulrich Keller wrote:
I have encountered a strange behaviour of as.integer() which does not
seem correct to me. Sorry if this is just an indication of me not
understanding floating point arithmetic.
.57 * 100
[1] 57
.29 * 100
[1] 29
So far, so good. But:
as.integer(.57 * 100)
[1] 56
as.integer(.29 * 100)
[1] 28
Then again:
all.equal(.57 * 100, as.integer(57))
[1] TRUE
all.equal(.29 * 100, as.integer(29))
[1] TRUE
This behaviour is the same in R 2.10.1 (Ubuntu and Windows) and 2.9.2
(Windows),
all 32 bit versions. Is this really intended?
Yes, as the man page states, non-integer values are truncated towards
zero. Normal printing rounds them. So .57*100, which is slightly less
than 57, is rounded to 57 for printing, but is truncated to 56 by
as.integer.
> .57*100 < 57
[1] TRUE
Duncan Murdoch
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