Hi Petr, Thank you for your answer.
I'm not sure how the empty index reflects what I'm showing in my example. If my function was emptySubset <- function(vec) vec[] I would then agree that this was the case. But I think it's different: I'm specifically telling my function that it should have two arguments ("vec" and "ix") subsettingFun <- function(vec, ix) vec[ix] and I guess why, within the function, it does not happen what happens on the command line: > ix Error: object 'ix' not found > letters[ix] Error: object 'ix' not found My "expectation" came from a matter of coherence, but probably I'm still missing something. Regards, Stefano 2016-02-04 15:39 GMT+01:00 PIKAL Petr <petr.pi...@precheza.cz>: > Hi > > Help page for ?"[" says > > An empty index selects all values: this is most often used to replace all > the entries but keep the attributes. > > and actually you function construction works with empty index > > > x<-c(1,2,5) > > letters[x] > [1] "a" "b" "e" > > letters[] > [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" > "r" "s" > [20] "t" "u" "v" "w" "x" "y" "z" > > It is sometimes useful not "expect" the program behavior but "inspect" why > it behaves differently. > > If you want your function to throw error when some arguments are missing > you need to do the check yourself and not rely on programming language. > > And BTW I did not know an answer before I inspected docs. > > Cheers > Petr > > > > -----Original Message----- > > From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Stefano > > de Pretis > > Sent: Thursday, February 04, 2016 11:00 AM > > To: r-help@r-project.org > > Subject: [R] Subset with missing argument within a function > > > > Hi all, > > > > I'm guessing what's the rationale behind this: > > > > > subsettingFun <- function(vec, ix) vec[ix] > > > subsettingFun(letters, c(1,2,5)) > > [1] "a" "b" "e" > > > subsettingFun(letters) > > [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" > > "q" > > "r" "s" > > [20] "t" "u" "v" "w" "x" "y" "z" > > > > If the argument "ix" is missing, I'm expecting an error not to return > > the > > variable "vec" as it is. > > > > I think this is VERY dangerous and does not help the development of > > reliable code and the debugging. > > > > Cheers, > > > > Stefano > > > > *Center for Genomic Science of IIT@SEMM* > > > > Stefano de Pretis, PhD > > > > *Postdoctoral fellow * > > > > [[alternative HTML version deleted]] > > > > ______________________________________________ > > 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. > > ________________________________ > Tento e-mail a jakékoliv k němu připojené dokumenty jsou důvěrné a jsou > určeny pouze jeho adresátům. > Jestliže jste obdržel(a) tento e-mail omylem, informujte laskavě > neprodleně jeho odesílatele. Obsah tohoto emailu i s přílohami a jeho kopie > vymažte ze svého systému. > Nejste-li zamýšleným adresátem tohoto emailu, nejste oprávněni tento email > jakkoliv užívat, rozšiřovat, kopírovat či zveřejňovat. > Odesílatel e-mailu neodpovídá za eventuální škodu způsobenou modifikacemi > či zpožděním přenosu e-mailu. > > V případě, že je tento e-mail součástí obchodního jednání: > - vyhrazuje si odesílatel právo ukončit kdykoliv jednání o uzavření > smlouvy, a to z jakéhokoliv důvodu i bez uvedení důvodu. > - a obsahuje-li nabídku, je adresát oprávněn nabídku bezodkladně přijmout; > Odesílatel tohoto e-mailu (nabídky) vylučuje přijetí nabídky ze strany > příjemce s dodatkem či odchylkou. > - trvá odesílatel na tom, že příslušná smlouva je uzavřena teprve > výslovným dosažením shody na všech jejích náležitostech. > - odesílatel tohoto emailu informuje, že není oprávněn uzavírat za > společnost žádné smlouvy s výjimkou případů, kdy k tomu byl písemně zmocněn > nebo písemně pověřen a takové pověření nebo plná moc byly adresátovi tohoto > emailu případně osobě, kterou adresát zastupuje, předloženy nebo jejich > existence je adresátovi či osobě jím zastoupené známá. > > This e-mail and any documents attached to it may be confidential and are > intended only for its intended recipients. > If you received this e-mail by mistake, please immediately inform its > sender. Delete the contents of this e-mail with all attachments and its > copies from your system. > If you are not the intended recipient of this e-mail, you are not > authorized to use, disseminate, copy or disclose this e-mail in any manner. > The sender of this e-mail shall not be liable for any possible damage > caused by modifications of the e-mail or by delay with transfer of the > email. > > In case that this e-mail forms part of business dealings: > - the sender reserves the right to end negotiations about entering into a > contract in any time, for any reason, and without stating any reasoning. > - if the e-mail contains an offer, the recipient is entitled to > immediately accept such offer; The sender of this e-mail (offer) excludes > any acceptance of the offer on the part of the recipient containing any > amendment or variation. > - the sender insists on that the respective contract is concluded only > upon an express mutual agreement on all its aspects. > - the sender of this e-mail informs that he/she is not authorized to enter > into any contracts on behalf of the company except for cases in which > he/she is expressly authorized to do so in writing, and such authorization > or power of attorney is submitted to the recipient or the person > represented by the recipient, or the existence of such authorization is > known to the recipient of the person represented by the recipient. > [[alternative HTML version deleted]] ______________________________________________ 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.