Hi everybody, given a fresh rgui.exe load on winxp OS, I enter (a minimal exaple) n <- 12.357531 Then the following command: n <- (n - floor(n))*10; n gives the following outputs: [1] 3.57531 [1] 5.7531 [1] 7.531 [1] 5.31 [1] 3.1 [1] 1 === still as expected [1] 10 === not expected, count with me: 1 - floor(1) is zero, times 10 gives 0, not 10!!!! [1] 10 === should stay forever zero (0) [1] 10 [1] 9.999998 [1] 9.999982 [1] 9.999821 [1] 9.998212 The sama happens with trunc(). e.g. (a minimal exaple) n <- 0.245 n <- (n - trunc(n))*10; n [1] 2.45 [1] 4.5 [1] 5 [1] 1.776357e-13 ===== zero expected!!! [1] 1.776357e-12 And I'm asking "what the heck?!" and where is the bug in my examples? Any suggestion well appreciated. p.s. The expression with floor() and trunc() are to be implemented in a function which gives a value equal precision order of the given number. e.g. 12.345 would have (-3), 12.1 would have (-1), 12 would have (0) and e.g. 12000 would have the order of the precision (4). Basically, it is the order of the last given non-zero digit. [[alternative HTML version deleted]]
That is not strange behaviour. It's a case of FAQ 7.31: http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f HTH, Thierry ---------------------------------------------------------------------------- ir. Thierry Onkelinx Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest Cel biometrie, methodologie en kwaliteitszorg / Section biometrics, methodology and quality assurance Gaverstraat 4 9500 Geraardsbergen Belgium tel. + 32 54/436 185 Thierry.Onkelinx at inbo.be www.inbo.be To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of. ~ Sir Ronald Aylmer Fisher The plural of anecdote is not data. ~ Roger Brinner The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data. ~ John Tukey -----Oorspronkelijk bericht----- Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] Namens ?rout?k Verzonden: donderdag 12 februari 2009 16:20 Aan: r-help at r-project.org Onderwerp: [R] trunc/floor a number -- strange bahaviour Hi everybody, given a fresh rgui.exe load on winxp OS, I enter (a minimal exaple) n <- 12.357531 Then the following command: n <- (n - floor(n))*10; n gives the following outputs: [1] 3.57531 [1] 5.7531 [1] 7.531 [1] 5.31 [1] 3.1 [1] 1 === still as expected [1] 10 === not expected, count with me: 1 - floor(1) is zero, times 10 gives 0, not 10!!!! [1] 10 === should stay forever zero (0) [1] 10 [1] 9.999998 [1] 9.999982 [1] 9.999821 [1] 9.998212 The sama happens with trunc(). e.g. (a minimal exaple) n <- 0.245 n <- (n - trunc(n))*10; n [1] 2.45 [1] 4.5 [1] 5 [1] 1.776357e-13 ===== zero expected!!! [1] 1.776357e-12 And I'm asking "what the heck?!" and where is the bug in my examples? Any suggestion well appreciated. p.s. The expression with floor() and trunc() are to be implemented in a function which gives a value equal precision order of the given number. e.g. 12.345 would have (-3), 12.1 would have (-1), 12 would have (0) and e.g. 12000 would have the order of the precision (4). Basically, it is the order of the last given non-zero digit. [[alternative HTML version deleted]] ______________________________________________ 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. Dit bericht en eventuele bijlagen geven enkel de visie van de schrijver weer en binden het INBO onder geen enkel beding, zolang dit bericht niet bevestigd is door een geldig ondertekend document. The views expressed in this message and any annex are purely those of the writer and may not be regarded as stating an official position of INBO, as long as the message is not confirmed by a duly signed document.
On 2/12/2009 10:20 AM, ?rout?k wrote:> Hi everybody, > > given a fresh rgui.exe load on winxp OS, I enter (a minimal exaple) > > n <- 12.357531 > > Then the following command: > n <- (n - floor(n))*10; n > > gives the following outputs: > [1] 3.57531 > [1] 5.7531 > [1] 7.531 > [1] 5.31 > [1] 3.1 > [1] 1 === still as expected > [1] 10 === not expected, count with me: 1 - floor(1) is zero, times > 10 gives 0, not 10!!!!You are assuming that when R prints "1", the value is exactly 1. But try this: > 0.999999999 [1] 1 > 0.999999999 == 1 [1] FALSE R rounds values when it prints them, because people don't want to see ugly output like this: > options(digits=18): > n <- 12.357531 > n <- (n - floor(n))*10; n [1] 3.5753100 > n <- (n - floor(n))*10; n [1] 5.75309999999998 > n <- (n - floor(n))*10; n [1] 7.530999999999821 > n <- (n - floor(n))*10; n [1] 5.30999999999821 > n <- (n - floor(n))*10; n [1] 3.099999999982117 > n <- (n - floor(n))*10; n [1] 0.999999999821171 And the reason you see such ugly output is because you are working with a number that can't be represented exactly in binary floating point. Duncan Murdoch> [1] 10 === should stay forever zero (0) > [1] 10 > [1] 9.999998 > [1] 9.999982 > [1] 9.999821 > [1] 9.998212 > > The sama happens with trunc(). > e.g. (a minimal exaple) > > n <- 0.245 > n <- (n - trunc(n))*10; n > [1] 2.45 > [1] 4.5 > [1] 5 > [1] 1.776357e-13 ===== zero expected!!! > [1] 1.776357e-12 > > And I'm asking "what the heck?!" and where is the bug in my examples? Any > suggestion well appreciated. > > p.s. The expression with floor() and trunc() are to be implemented in a > function which gives a value equal precision order of the given number. e.g. > 12.345 would have (-3), 12.1 would have (-1), 12 would have (0) and e.g. > 12000 would have the order of the precision (4). Basically, it is the order > of the last given non-zero digit. > > [[alternative HTML version deleted]] > > ______________________________________________ > 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.
Resolved.
nchar(unlist(strsplit(as.character(n),"\\.")))[2]
in the function:
NumberPrecision <- function(n) {
PocetCyklu <- 0
if(n != round(n)) {
PocetCyklu <- nchar(unlist(strsplit(n,"\\.")))[2]
}
else {
while(n == round(n)) {
n <- n/10
PocetCyklu <- PocetCyklu + 1
}
PocetCyklu <- PocetCyklu - 1
#}
PocetCyklu
}
for 130000 the precision of the given value is the last given digit -- 5,
for 12.345 it gives 3. Perfect.
Regards, Z
Thank you for the thoughtful conversation.
---------- Forwarded message ----------
From: Žroutík <zroutik@gmail.com>
Date: Fri, Feb 13, 2009 at 7:32 AM
Subject: Re: [R] trunc/floor a number -- strange bahaviour
To: Duncan Murdoch <murdoch@stats.uwo.ca>
Thank you Duncan, and Thierry, to you, too, for the quick responses.
In the FAQ, there is a different example, IMO. The value sqrt(2) is created
by some function and is irrational -- I do understand in
"never-ending"
numbers programs do have to cut some digits off, therefore a mismatch. But
in my example the given value is fix (it is written into an input file by a
user) and there is always a fix number of digits and the number is not
irrational.
I do not understand how can the given/fix number 0.0001 be abruptly
represented as 0.000099999.
You say it's about binary floating point. But this is way the binary
floating point was created, for real ending values, isn't it so?
12.34 is represented as 1234 (integer) times ten (integer) to the minus 2
(integer). (n - floor(n))*10 Minus floor(12) (integer), times ten gives 34
(integer) times ten to the -1 (integer).
Is there any way how can I check on not to crush in such a problems. I
remind you, I do not count with irrational or other "neverending"
numbers.
Regrads,
Zroutik
On Thu, Feb 12, 2009 at 4:44 PM, Duncan Murdoch
<murdoch@stats.uwo.ca>wrote:
> On 2/12/2009 10:20 AM, Žroutík wrote:
>
>> Hi everybody,
>>
>> given a fresh rgui.exe load on winxp OS, I enter (a minimal exaple)
>>
>> n <- 12.357531
>>
>> Then the following command:
>> n <- (n - floor(n))*10; n
>>
>> gives the following outputs:
>> [1] 3.57531
>> [1] 5.7531
>> [1] 7.531
>> [1] 5.31
>> [1] 3.1
>> [1] 1 === still as expected
>> [1] 10 === not expected, count with me: 1 - floor(1) is zero,
times
>> 10 gives 0, not 10!!!!
>>
>
> You are assuming that when R prints "1", the value is exactly 1.
But try
> this:
>
> > 0.999999999
> [1] 1
> > 0.999999999 == 1
> [1] FALSE
>
> R rounds values when it prints them, because people don't want to see
ugly
> output like this:
>
> > options(digits=18):
> > n <- 12.357531
> > n <- (n - floor(n))*10; n
> [1] 3.5753100
> > n <- (n - floor(n))*10; n
> [1] 5.75309999999998
> > n <- (n - floor(n))*10; n
> [1] 7.530999999999821
> > n <- (n - floor(n))*10; n
> [1] 5.30999999999821
> > n <- (n - floor(n))*10; n
> [1] 3.099999999982117
> > n <- (n - floor(n))*10; n
> [1] 0.999999999821171
>
> And the reason you see such ugly output is because you are working with a
> number that can't be represented exactly in binary floating point.
>
> Duncan Murdoch
>
> [1] 10 === should stay forever zero (0)
>> [1] 10
>> [1] 9.999998
>> [1] 9.999982
>> [1] 9.999821
>> [1] 9.998212
>>
>> The sama happens with trunc().
>> e.g. (a minimal exaple)
>>
>> n <- 0.245
>> n <- (n - trunc(n))*10; n
>> [1] 2.45
>> [1] 4.5
>> [1] 5
>> [1] 1.776357e-13 ===== zero expected!!!
>> [1] 1.776357e-12
>>
>> And I'm asking "what the heck?!" and where is the bug in
my examples? Any
>> suggestion well appreciated.
>>
>> p.s. The expression with floor() and trunc() are to be implemented in a
>> function which gives a value equal precision order of the given number.
>> e.g.
>> 12.345 would have (-3), 12.1 would have (-1), 12 would have (0) and
e.g.
>> 12000 would have the order of the precision (4). Basically, it is the
>> order
>> of the last given non-zero digit.
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@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.
>>
>
>
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