[R] converting numeric to integer

[Thomas Mang]

Hi,

The problem is, x might be negative. If x == -6.9999999, the result 
should be -7, not -6. That's why my original proposal had the 
ifelse-condition (one could alternatively write sign(x) * 0.5, BTW.
I agree however that in my proposal, the round(x) is redundant, one can 
use x itself as left-hand argument for the sum operation. Is there 
however still a more 'elegant' way ?

thanks,
Thomas



Gabor Grothendieck wrote:
> Try:
> 
> as.integer(x + 0.5)
> 
> assuming the calculation error is less than 0.5 .
> 
> On Sat, May 16, 2009 at 2:49 PM, 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
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>