converting numeric to integer

Hi,

Well, also not quite.
Suppose x = 5.00000000001 (in finite binary represenation). Then I want x ==
5, but that is of course an integer which is now less than the original
numeral.

Your code would turn it into 6; ?moreover, your code would still work on
numeric-values, so once it gets to the interger-conversion we are back at
where the problem started, namely at the issue of finite floating-point
representations, which might, or might not, yield the desired integer after
the decimal digits have been truncated.

BTW, do you know why sometimes replys do not appear in the newsgroups ->
mine to yours is not there, equally not your last response (althought the
later might of course be the resuld because I made a mistak. in the first
step....)

cheers and thanks,
Thomas


Linlin Yan wrote:

I see. What you want is the integer with same sign as the original
numeral, and whose absolute value is the least integer which is not
less than absolute value of the original numeral. Am I right? I am
afraid that there may not be any single function could work it out.
But I could give the following expression:
sign(x) * ceiling(abs(x)),
which may be a little clearer.

On Sun, May 17, 2009 at 2:02 PM, Thomas Mang <Thomas.Mang at fiwi.at> wrote:

Hi,

ceiling would do the wrong thing for negative values. If x = -4.9999999,
the
wanted result would be -5, but ceiling makes a -4 out of it.

bye,
Thomas

Linlin Yan wrote:

How about ceiling(x), which return the smallest integer not less than x?

On Sun, May 17, 2009 at 2:49 AM, Thomas Mang <thomas.mang at fiwi.at>
wrote:

Hello,

Suppose I have x, which is a variable of class numeric. The
calculations
performed to yield x imply that mathematically it should be an integer
,
but
due to round-off errors, it might not be (and so in either direction).
The
error is however small, so round(x) will yield the appropriate integer
value. Moreover, this integer values is guaranteed to be representable
by
an
'integer' class, that is -2^31 < x < 2^31, and logically it is an
integer
anyway. So I want to convert x from class 'numeric' to 'integer'. What
is
the most elegant, but always correct way, to achieve this conversion ?

What comes to mind is of course something along:

x = as.integer(round(x))

I am, however, not sure if this always works, because I do not know if
the
round-function is guaranteed to return a numeric value which, in finite
binary representation, is always >= the underlying mathematical
integer.
If
that is however guaranteed, that would of course be a simple + elegant
one.

An alternative I came up with is:

x = as.integer(round(x) + ifelse(x >= 0, 0.5, -0.5))
Where I explicitly add a bit to ensure the finite binary representation
must
be >= the underlying integer, and then truncate the decimal digits.
IMO, this one is always guaranteed to work, at least within the
numerical
range of what integers are limited to anyway.


What's your opinion on the issue ?
Any other solution ?

Thanks a lot in advance and cheers,
Thomas