Thank you very much for your answer. Yes, meanwhile I found out … Plus, that index that which() is returning applied on the matrix is calculated as:
matrix[rowIndices + nrow(matrix) * (colIndices - 1)] thanks again for your help From: William Dunlap <wdun...@tibco.com> Sent: Thursday, April 25, 2019 10:03 AM To: Nitu, Laurentiu <laurentiu.n...@fraserhealth.ca> Cc: r-help@r-project.org Subject: Re: [R] Question about addressing a data frame is.na<http://is.na>(DF) is a matrix for a data.frame DF. The semantics of '[" are different for matrices and data.frame and that can cause confusion > DF <- data.frame(X=c(101,NA,NA), Y=c("one","two",NA), > row.names=c("i","ii","iii")) > is.na<http://is.na>(DF) # returns a matrix when given a data.frame X Y i FALSE FALSE ii TRUE FALSE iii TRUE TRUE > which(is.na<http://is.na>(DF)) # returns a vector when given a data.frame [1] 2 3 6 > which(is.na<http://is.na>(DF), arr.ind=TRUE) # returns a > length(dim(matrix))-column matrix when given an array row col ii 2 1 iii 3 1 iii 3 2 > DF[!is.na<http://is.na>(DF)] # as.matrix(DF)[ > !is.na<http://is.na>(as.matrix(DF)) ] [1] "101" "one" "two" Bill Dunlap TIBCO Software wdunlap tibco.com<http://tibco.com> On Thu, Apr 25, 2019 at 9:27 AM Nitu, Laurentiu <laurentiu.n...@fraserhealth.ca<mailto:laurentiu.n...@fraserhealth.ca>> wrote: Hello, I have this data frame [algae] in the package DMwR. I thought I understand how to refer an element but I cannot explain... is.na<http://is.na>(algae) is giving us the a logical vector with TRUE being the na's. which(is.na<http://is.na>(algae)) gives the positions on the elements in the data frame where is.na<http://is.na> returns TRUE. However which(is.na<http://is.na>(algae)) returns [1] 648 838 862 1055 1056 1057 1058 1059 1060 1061 1062 1161 1199 1262 1399 1462 1599 1662 1799 1828 1999 2055 2056 2057 2058 2059 2060 2061 2062 2063 [31] 2116 2184 2199 Weirs since: > dim(algae) [1] 200 18 If I refer back algae[which(is.na<http://is.na>(algae))) I get a vector of NA's... What are the values returned by which(is.na<http://is.na>(algae))? Thanks a lot for your help [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org<mailto: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. [[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.
