Hello, I want to get the differences when comparing 2 vectors, by pair (element by element). I'd like to get TRUEs when: - the two compared elements are different and non-missing (like `!=` does) - one element is missing and the other is not missing (unfortunatelly `!=` gives NA and not TRUE) Note that I don't want to get TRUEs when both are missing. NA or FALSE are fine. Given a and b:> a <- c(1, 2, 3, NA, NA) > b <- c(1, 9, NA, 4 , NA)The only solution I found is:> a != b | (is.na(a) != is.na(b))[1] FALSE TRUE TRUE TRUE NA Is there a single function which can do the same? I searched for other comparison tools but found nothing relevant. And I would like also to avoid using `!=` because I'm often comparing floating numbers computed by different algorithms (so rounded differently). I found identical() interesting (for exemple, !(identical(NA, 99)) gives TRUE) but the result of !(identical(a, b) is a single logical, not a vector of logicals. Many thanks in advance for your help. P.S. I am new to R, coming from SAS. Actually, I'm looking for the R function that replicates the SAS instruction: if a ^= b; [[alternative HTML version deleted]]
Fabien: In general, R's philosophy as a programming language is that it should make it easy (and maybe efficient) to do the (data analysis) things you want to do, not necessarily provide all pre-packaged procedures (although with all the packages, it seems to come close to that!). So the following seems to fall into that paradigm (using your example a and b)> tol <- 1e-15> xor(is.na(a),is.na(b)) | (abs(b-a) > tol)[1] FALSE TRUE TRUE TRUE NA As you noted, defining equality of floating point numbers is a tricky business, so that you may prefer some other approach to that which I used. There may well be "pre-packaged" ways to do this, but I didn't look. You might try searching rseek.org for "defining numerical equality in R" or some such to see. Cheers, Bert Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Tue, Oct 4, 2016 at 9:51 AM, fabien verger <fabien.verger at gmail.com> wrote:> Hello, > > I want to get the differences when comparing 2 vectors, by pair (element by > element). > I'd like to get TRUEs when: > - the two compared elements are different and non-missing (like `!=` does) > - one element is missing and the other is not missing (unfortunatelly `!=` > gives NA and not TRUE) > Note that I don't want to get TRUEs when both are missing. NA or FALSE are > fine. > > Given a and b: >> a <- c(1, 2, 3, NA, NA) >> b <- c(1, 9, NA, 4 , NA) > > The only solution I found is: > >> a != b | (is.na(a) != is.na(b)) > [1] FALSE TRUE TRUE TRUE NA > > Is there a single function which can do the same? > I searched for other comparison tools but found nothing relevant. > > And I would like also to avoid using `!=` because I'm often comparing > floating numbers computed by different algorithms (so rounded differently). > > I found identical() interesting (for exemple, !(identical(NA, 99)) gives > TRUE) but the result of !(identical(a, b) is a single logical, not a vector > of logicals. > > Many thanks in advance for your help. > P.S. I am new to R, coming from SAS. Actually, I'm looking for the R > function that replicates the SAS instruction: if a ^= b; > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at 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.
Hi,
A couple of comments:
1. Fabien, since you are transitioning from SAS, you may find the resources that
Bob Muenchen has made available to be of value:
http://r4stats.com/ <http://r4stats.com/>
There is a free download (PDF) of an earlier version of his book available via
his web site as well.
2. Presuming that Bert's approach satisfies your functional requirements in
this case, you can encapsulate his code into a function that you might find
easier to use moving forward. For example:
IsDiff <- function(a, b, tol = 1e-15) {
xor(is.na(a),is.na(b)) | (abs(b-a) > tol)
}
a <- c(1, 2, 3, NA, NA)
b <- c(1, 9, NA, 4 , NA)
> IsDiff(a, b)
[1] FALSE TRUE TRUE TRUE NA
Of course, you can call the function anything you wish, as long as it is a legal
object name in R.
You could even create a new infix operator along the lines of the following,
with the restriction that this approach can only take two arguments, so you
would hard code the tolerance level in the function body:
"%ID%" <- function(a, b) {
xor(is.na(a),is.na(b)) | (abs(b-a) > 1e-15)
}
> a %ID% b
[1] FALSE TRUE TRUE TRUE NA
Bear in mind that a substantial portion of R is written in R itself, with a core
set of functionality in C and FORTRAN where performance is materially enhanced
by the use of compiled code. Thus, extending R's functionality, as Bert
notes, is typically done by useRs encapsulating enhanced functionality in new R
functions and the now thousands of packages on CRAN generally follow that same
paradigm for specific applications.
Regards,
Marc Schwartz
> On Oct 4, 2016, at 12:33 PM, Bert Gunter <bgunter.4567 at gmail.com>
wrote:
>
> Fabien:
>
> In general, R's philosophy as a programming language is that it should
> make it easy (and maybe efficient) to do the (data analysis) things
> you want to do, not necessarily provide all pre-packaged procedures
> (although with all the packages, it seems to come close to that!). So
> the following seems to fall into that paradigm (using your example a
> and b)
>
>> tol <- 1e-15
>
>> xor(is.na(a),is.na(b)) | (abs(b-a) > tol)
> [1] FALSE TRUE TRUE TRUE NA
>
>
> As you noted, defining equality of floating point numbers is a tricky
> business, so that you may prefer some other approach to that which I
> used. There may well be "pre-packaged" ways to do this, but I
didn't
> look. You might try searching rseek.org for "defining numerical
> equality in R" or some such to see.
>
>
> Cheers,
> Bert
> Bert Gunter
>
> "The trouble with having an open mind is that people keep coming along
> and sticking things into it."
> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip
)
>
>
> On Tue, Oct 4, 2016 at 9:51 AM, fabien verger <fabien.verger at
gmail.com> wrote:
>> Hello,
>>
>> I want to get the differences when comparing 2 vectors, by pair
(element by
>> element).
>> I'd like to get TRUEs when:
>> - the two compared elements are different and non-missing (like `!=`
does)
>> - one element is missing and the other is not missing (unfortunatelly
`!=`
>> gives NA and not TRUE)
>> Note that I don't want to get TRUEs when both are missing. NA or
FALSE are
>> fine.
>>
>> Given a and b:
>>> a <- c(1, 2, 3, NA, NA)
>>> b <- c(1, 9, NA, 4 , NA)
>>
>> The only solution I found is:
>>
>>> a != b | (is.na(a) != is.na(b))
>> [1] FALSE TRUE TRUE TRUE NA
>>
>> Is there a single function which can do the same?
>> I searched for other comparison tools but found nothing relevant.
>>
>> And I would like also to avoid using `!=` because I'm often
comparing
>> floating numbers computed by different algorithms (so rounded
differently).
>>
>> I found identical() interesting (for exemple, !(identical(NA, 99))
gives
>> TRUE) but the result of !(identical(a, b) is a single logical, not a
vector
>> of logicals.
>>
>> Many thanks in advance for your help.
>> P.S. I am new to R, coming from SAS. Actually, I'm looking for the
R
>> function that replicates the SAS instruction: if a ^= b;
[[alternative HTML version deleted]]
The all.equal function returns TRUE if two objects are pretty similar to one another and a textual description of the differences if not. Use isTRUE on its output if you just want a TRUE/FALSE answer. > all.equal(c(1,2*(1+.Machine$double.eps),NaN), c(1,2,NaN)) [1] TRUE > all.equal(c(1,2*(1+.Machine$double.eps),NaN), c(1,2,NaN), tolerance=0) [1] "Mean relative difference: 2.220446e-16" > isTRUE(all.equal(c(1,2*(1+.Machine$double.eps),NaN), c(1,2,NaN), tolerance=0)) [1] FALSE > all.equal(c(a=1, b=2), c(x=1, b=2)) [1] "Names: 1 string mismatch" Bill Dunlap TIBCO Software wdunlap tibco.com On Tue, Oct 4, 2016 at 9:51 AM, fabien verger <fabien.verger at gmail.com> wrote:> Hello, > > I want to get the differences when comparing 2 vectors, by pair (element by > element). > I'd like to get TRUEs when: > - the two compared elements are different and non-missing (like `!=` does) > - one element is missing and the other is not missing (unfortunatelly `!=` > gives NA and not TRUE) > Note that I don't want to get TRUEs when both are missing. NA or FALSE are > fine. > > Given a and b: > > a <- c(1, 2, 3, NA, NA) > > b <- c(1, 9, NA, 4 , NA) > > The only solution I found is: > > > a != b | (is.na(a) != is.na(b)) > [1] FALSE TRUE TRUE TRUE NA > > Is there a single function which can do the same? > I searched for other comparison tools but found nothing relevant. > > And I would like also to avoid using `!=` because I'm often comparing > floating numbers computed by different algorithms (so rounded differently). > > I found identical() interesting (for exemple, !(identical(NA, 99)) gives > TRUE) but the result of !(identical(a, b) is a single logical, not a vector > of logicals. > > Many thanks in advance for your help. > P.S. I am new to R, coming from SAS. Actually, I'm looking for the R > function that replicates the SAS instruction: if a ^= b; > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at 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. >[[alternative HTML version deleted]]
Bill, I had initially thought of using all.equal() along with isTrue(), however Fabien's desire for a pairwise element based approach, along with the specific NA handling steered me away from it and towards code along the lines of what Bert had offered, which builds on the basic notion of approximate numeric equality as used in all.equal(). Regards, Marc> On Oct 4, 2016, at 2:02 PM, William Dunlap via R-help <r-help at r-project.org> wrote: > > The all.equal function returns TRUE if two objects are pretty similar to > one another and a textual description of the differences if not. Use > isTRUE on its output if you just want a TRUE/FALSE answer. > >> all.equal(c(1,2*(1+.Machine$double.eps),NaN), c(1,2,NaN)) > [1] TRUE >> all.equal(c(1,2*(1+.Machine$double.eps),NaN), c(1,2,NaN), tolerance=0) > [1] "Mean relative difference: 2.220446e-16" >> isTRUE(all.equal(c(1,2*(1+.Machine$double.eps),NaN), c(1,2,NaN), > tolerance=0)) > [1] FALSE >> all.equal(c(a=1, b=2), c(x=1, b=2)) > [1] "Names: 1 string mismatch" > > > > Bill Dunlap > TIBCO Software > wdunlap tibco.com > > On Tue, Oct 4, 2016 at 9:51 AM, fabien verger <fabien.verger at gmail.com> > wrote: > >> Hello, >> >> I want to get the differences when comparing 2 vectors, by pair (element by >> element). >> I'd like to get TRUEs when: >> - the two compared elements are different and non-missing (like `!=` does) >> - one element is missing and the other is not missing (unfortunatelly `!=` >> gives NA and not TRUE) >> Note that I don't want to get TRUEs when both are missing. NA or FALSE are >> fine. >> >> Given a and b: >>> a <- c(1, 2, 3, NA, NA) >>> b <- c(1, 9, NA, 4 , NA) >> >> The only solution I found is: >> >>> a != b | (is.na(a) != is.na(b)) >> [1] FALSE TRUE TRUE TRUE NA >> >> Is there a single function which can do the same? >> I searched for other comparison tools but found nothing relevant. >> >> And I would like also to avoid using `!=` because I'm often comparing >> floating numbers computed by different algorithms (so rounded differently). >> >> I found identical() interesting (for exemple, !(identical(NA, 99)) gives >> TRUE) but the result of !(identical(a, b) is a single logical, not a vector >> of logicals. >> >> Many thanks in advance for your help. >> P.S. I am new to R, coming from SAS. Actually, I'm looking for the R >> function that replicates the SAS instruction: if a ^= b; >> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> R-help at 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. >> > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at 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.