Thanks Matthias for the details! Ivan
-- Dr. Ivan Calandra TraCEr, laboratory for Traceology and Controlled Experiments MONREPOS Archaeological Research Centre and Museum for Human Behavioural Evolution Schloss Monrepos 56567 Neuwied, Germany +49 (0) 2631 9772-243 https://www.researchgate.net/profile/Ivan_Calandra On 31/03/2020 16:30, Prof. Dr. Matthias Kohl wrote: > should have added: dim(x)[2L] -> length(x) > > Am 31.03.20 um 16:21 schrieb Prof. Dr. Matthias Kohl: >> Dear Ivan, >> >> if I enter ncol in the console, I get >> >> function (x) >> dim(x)[2L] >> <bytecode: 0x5559e9429030> >> <environment: namespace:base> >> >> indicating that function dim is called. Function dim has a method for >> data.frame; see methods("dim"). >> >> The dim-method for data.frame is >> >> dim.data.frame >> function (x) >> c(.row_names_info(x, 2L), length(x)) >> <bytecode: 0x5559eb80da40> >> <environment: namespace:base> >> >> Hence, it calls length on the provided data.frame. In addition, some >> "magic" with .row_names_info is performed, where >> >> base:::.row_names_info >> function (x, type = 1L) >> .Internal(shortRowNames(x, type)) >> <bytecode: 0x5559ece50160> >> <environment: namespace:base> >> >> Best >> Matthias >> >> Am 31.03.20 um 16:10 schrieb Ivan Calandra: >>> Thanks Ivan for the answer. >>> >>> So it confirms my first thought that these two functions are equivalent >>> when applied to a "simple" data.frame. >>> >>> The reason I was asking is because I have gotten used to use >>> length() in >>> my scripts. It works perfectly and I understand it easily. But to be >>> honest, ncol() is more intuitive to most users (especially the novice) >>> so I was thinking about switching to using this function instead >>> (all my >>> data.frames are created from read.csv() or similar functions so there >>> should not be any issue). But before doing that, I want to be sure that >>> it is not going to create unexpected results. >>> >>> Thank you, >>> Ivan >>> >>> -- >>> Dr. Ivan Calandra >>> TraCEr, laboratory for Traceology and Controlled Experiments >>> MONREPOS Archaeological Research Centre and >>> Museum for Human Behavioural Evolution >>> Schloss Monrepos >>> 56567 Neuwied, Germany >>> +49 (0) 2631 9772-243 >>> https://www.researchgate.net/profile/Ivan_Calandra >>> >>> On 31/03/2020 16:00, Ivan Krylov wrote: >>>> On Tue, 31 Mar 2020 14:47:54 +0200 >>>> Ivan Calandra <calan...@rgzm.de> wrote: >>>> >>>>> On a simple data.frame (i.e. each element is a vector), ncol() and >>>>> length() will give the same result. >>>>> Are they just equivalent on such objects, or are they differences in >>>>> some cases? >>>> I am not aware of any exceptions to ncol(dataframe)==length(dataframe) >>>> (in fact, ncol(x) is dim(x)[2L] and ?dim says that dim(dataframe) >>>> returns c(length(attr(dataframe, 'row.names')), >>>> length(dataframe))), but >>>> watch out for AsIs columns which can have columns of their own: >>>> >>>> x <- data.frame(I(volcano)) >>>> dim(x) >>>> # [1] 87 1 >>>> length(x) >>>> # [1] 1 >>>> dim(x[,1]) >>>> # [1] 87 61 >>>> >>>> >>> >>> ______________________________________________ >>> 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-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.
