Hi Above what was said
data(data[,4] == 1, c(1 2 4)) Error: unexpected numeric constant in "data(data[,4] == 1, c(1 2" is not valid syntax as it assume that data is a function and c(1 2 4) is also not correct syntax (I wonder if commands in MATLAB are such free form). And I am a little puzzled what means to bring 3 columns together. Calculate sum? Paste respective values in mentioned 3 columns. Anyway, if you want to select only first n rows you should use something like data[1:20,][data[1:20,4]==1,c(1,2,4)] or data[which(data[1:20,4]==1), c(1,2,4)] You should also be careful with "==" if you compare numbers, especially fractions and to select without "with" if your data contain NA values in respective columns. Cheers Petr > -----Original Message----- > From: R-help [mailto:r-help-boun...@r-project.org] On Behalf Of Erich > Subscriptions > Sent: Monday, February 27, 2017 1:30 PM > To: Tunga Kantarcı <tungakanta...@gmail.com> > Cc: R-help <r-help@r-project.org> > Subject: Re: [R] Selecting rows and columns of a data frame using relational > operators > > The answer is simple > > data[,4] == 1 produces a logical vector of length nrow(data) and the > subsetting mechanism for data frames in R needs a vector of the same length > as the data frame has rows. > > data[1:20,4] == 1 > produces a data frame of length 20, and if this is not the length of data. > So R applies its standard procedure, it repeats this vector as often as needed > to get a vector of length == nrow(data) > > > Th following code illustrates what is happening > > data <- > data.frame(x=rnorm(100),y=rnorm(100),z=rnorm(100),a=rep(c(1,2,1,2),c(2,4 > 8,2,48))) > > vec1 <- data[,4]==1 > vec2 <- data[1:20,4]==1 > > > > On 27 Feb 2017, at 13:07, Tunga Kantarcı <tungakanta...@gmail.com> > wrote: > > > > Consider a data frame named data. data contains 4 columns and 1000 > > rows. Say the aim is to bring together columns 1, 2, and 4, if the > > values in column 4 is equal to 1. We could use the syntax > > > > data(data[,4] == 1, c(1 2 4)) > > > > for this purpose. Suppose now that the aim is to bring together > > columns 1, 2, and 4, if the values in column 4 is equal to 1, for the > > first 20 rows of column 4. We could use the syntax > > > > data(data[1:20,4] == 1, c(1 2 4)) > > > > for this purpose. However, this does not produce the desired result. > > This is surprising at least for someone coming from MATLAB because > > MATLAB produces what is desired. > > > > Question 1: The code makes sense but why does it not produce what we > > expect it to produce? > > > > Question 2: What code is instead suitable? > > > > ______________________________________________ > > 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. ________________________________ Tento e-mail a jakékoliv k němu připojené dokumenty jsou důvěrné a jsou určeny pouze jeho adresátům. 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