Re: [R] gmp::bigq vs. MASS::fractions
Hello, Am 07.01.23 um 17:55 schrieb Ivan Krylov: > What do you need the fractions for? > When writing tasks for statistics exams, I try to avoid non-terminal intermediate results. Students might round them and arrive at a final result that might be slightly different from the true value. Although the exam package supports a tolerance for checking the result, this could be problematic. To check if a number is non-terminal, I calculate a fraction representation and check if the denominator can be expressed by 2^p 5^q. @Enrico: When I started developing assignments a few years ago, I was not familiar with gmp. :( Thanks Sigbert __ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
Re: [R] gmp::bigq vs. MASS::fractions
On Sat, 07 Jan 2023, Sigbert Klinke writes:
> Hi,
>
> has someone experience which routine should be used for
> creating fractional numbers? The two conversion
> routines deliver different results
>
>> x <- (0:7)/7
>
>> MASS::fractions(x)
>
> [1] 0 1/7 2/7 3/7 4/7 5/7 6/7 1
>
>> gmp::as.bigq(x)
>
> Big Rational ('bigq') object of length 8:
>
> [1] 0 2573485501354569/18014398509481984
> 2573485501354569/9007199254740992
>
> [4] 7720456504063707/18014398509481984
> 2573485501354569/4503599627370496
> 6433713753386423/9007199254740992
>
> [7] 7720456504063707/9007199254740992 1
>
> Following the example I would compute my fractional
> numbers with MASS::fractions and store them for further
> processing as Big Rational.
>
> Thanks Sigbert
>
'gmp' allows you to create the fractions directly:
gmp::as.bigq(n = 0:7, d = 7)
## Big Rational ('bigq') object of length 8:
## [1] 0 1/7 2/7 3/7 4/7 5/7 6/7 1
--
Enrico Schumann
Lucerne, Switzerland
http://enricoschumann.net
__
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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.
Re: [R] gmp::bigq vs. MASS::fractions
On Sat, 7 Jan 2023 17:29:35 +0100
Sigbert Klinke wrote:
> > x <- (0:7)/7
>
> > MASS::fractions(x)
>
> [1] 0 1/7 2/7 3/7 4/7 5/7 6/7 1
>
> > gmp::as.bigq(x)
>
> Big Rational ('bigq') object of length 8:
>
> [1] 0
> 2573485501354569/18014398509481984 2573485501354569/9007199254740992
>
> [4] 7720456504063707/18014398509481984
> 2573485501354569/4503599627370496 6433713753386423/9007199254740992
>
> [7] 7720456504063707/9007199254740992 1
That's a consequence of the way fractions are internally represented
inside most modern processors. In short, gmp::as.bigq takes the red
pill and shows you the reality as it is (all fractions have a limited
number of significant digits -- 52 binary digits -- and are required to
have a denominator that's a power of two), while MASS::fractions tries
to guess what the original number might have been before an imprecise
approximation of k/7 had been computed. (Since 7 is not a power of 2,
only 0 and 1 have an exact representation in your example.)
For more information, see R FAQ 7.31:
https://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f
What do you need the fractions for?
--
Best regards,
Ivan
__
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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.
[R] gmp::bigq vs. MASS::fractions
Hi,
has someone experience which routine should be used for creating
fractional numbers? The two conversion routines deliver different results
> x <- (0:7)/7
> MASS::fractions(x)
[1] 0 1/7 2/7 3/7 4/7 5/7 6/7 1
> gmp::as.bigq(x)
Big Rational ('bigq') object of length 8:
[1] 0
2573485501354569/18014398509481984 2573485501354569/9007199254740992
[4] 7720456504063707/18014398509481984 2573485501354569/4503599627370496
6433713753386423/9007199254740992
[7] 7720456504063707/9007199254740992 1
Following the example I would compute my fractional numbers with
MASS::fractions and store them for further processing as Big Rational.
Thanks Sigbert
__
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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.
