Hi Javad, In that case, just modify the function to extract the rows with both the minimum and maximum Q from each station
df1<-read.table(text="Code Y M D Q N O 41003 81 1 19 0.16 7.17 2.5 41003 77 9 22 0.197 6.8 2.2 41003 79 7 28 0.21 4.7 6.2 41005 79 8 17 0.21 5.5 7.2 41005 80 10 30 0.21 6.84 2.6 41005 80 12 20 0.21 6.84 2.4 41005 79 6 14 0.217 5.61 3.55 41009 79 2 21 0.218 5.56 4.04 41009 79 5 27 0.218 6.4 3.12 41009 80 11 29 0.22 6.84 2.8 41009 78 5 28 0.232 6 3.2 41009 81 8 20 0.233 6.39 1.6 41009 79 9 30 0.24 5.6 7.5 41017 79 10 20 0.24 5.3 7.1 41017 80 7 30 0.24 6.73 2.6", stringsAsFactors=FALSE,header=TRUE) # define a function that returns the desired rows minmaxQrow<-function(x) return(x[c(which.min(x$Q),which.max(x$Q)),]) # apply the function to the data frame df1a<-by(df1,df1$Code,minmaxQrow) # set the result to the first element of the list df1b<-df1a[[1]] # rbind the remaining rows for(i in 2:length(df1a)) df1b<-rbind(df1b,df1a[[i]]) # display the result df1b Jim On Fri, Aug 26, 2022 at 5:25 AM javad bayat <j.bayat...@gmail.com> wrote: > ... > I think I should explain more about my request. I had a large data frame > (11059 rows and 16 columns). The Code column represented the stations code, > totally the number of stations were 128. At each station I had many > measured variables, like Q and N and O, and these variables were measured > in different years and days. The days that data were measured were > different for each station, and due to this reason I had different rows for > stations. For example, station number one (41009) had 158 rows and station > number 2 (41011) had 113 rows. Note that the station's codes are not in > order format (e.g smallest to largest). > Back to my request, I wanted to extract the minimum value of the Q for each > station (based on the Code column). The problem was that I wanted to have > other column values which were measured for this minimum of the Q. > I hope my explanation was clear enough. As I said before, I used the Rui's > codes and I got what I wanted. Although, other solutions provided by others > were all correct. > ______________________________________________ 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.
