Dear R-Help List, I would like to use an iterator to read a file filtering some selected lines according to the line name in order to use after a foreach loop. I wanted to use the checkFunc argument as the following example found on internet to select only prime numbers :
| iprime <- ||iter||(1:100, checkFunc = ||function||(n) ||isprime||(n))| |(https://datawookie.netlify.app/blog/2013/11/iterators-in-r/) <https://datawookie.netlify.app/blog/2013/11/iterators-in-r/>| but the checkFunc argument seems not to be available with the function ireadLines (package iterators). So, I did the code below to solve my problem but I am sure that I miss something to use iterators with files. Since I found nothing on the web about ireadLines and the checkFunc argument, could somebody help me to understand how we have to use iterator (and foreach loop) on files keeping only selected lines ? Thank you very much Laurent Presently here is my code: ## mock file to read: test.txt ## # Time 0 0.000999 0.001999 0.002998 0.003998 0.004997 0.005997 0.006996 0.007996 # N023 -0.031323 -0.035026 -0.029759 -0.024886 -0.024464 -0.026816 -0.03369 -0.041067 -0.038747 # N053 -0.014083 -0.004741 0.001443 -0.010152 -0.012996 -0.005337 -0.008738 -0.015094 -0.012104 # N123 -0.019008 -0.013494 -0.01318 -0.029208 -0.032748 -0.020243 -0.015089 -0.014439 -0.011681 # N163 -0.054023 -0.049345 -0.037158 -0.04112 -0.044612 -0.036953 -0.036061 -0.044516 -0.046436 # N193 -0.022171 -0.022384 -0.022338 -0.023304 -0.022569 -0.021827 -0.021996 -0.021755 -0.021846 # sensors to keep sensors <- c("N053", "N163") library(iterators) library(rlist) file_name <- "test.txt" con_obj <- file( file_name , "r") ifile <- ireadLines( con_obj , n = 1 ) ## I do not do a loop for the example res <- list() r <- get_Lines_iter( ifile , sensors) res <- list.append( res , r ) res r <- get_Lines_iter( ifile , sensors) res <- list.append( res , r ) res r <- get_Lines_iter( ifile , sensors) do.call("cbind",res) ## the function get_Lines_iter to select and process the line get_Lines_iter <- function( iter , sensors, sep = '\t', quiet = FALSE){ ## read the next record in the iterator r = try( nextElem(iter) ) while( TRUE ){ if( class(r) == "try-error") { return( stop("The iterator is empty") ) } else { ## split the read line according to the separator r_txt <- textConnection(r) fields <- scan(file = r_txt, what = "character", sep = sep, quiet = quiet) ## test if we have to keep the line if( fields[1] %in% sensors){ ## data processing for the selected line (for the example transformation in dataframe) n <- length(fields) x <- data.frame( as.numeric(fields[2:n]) ) names(x) <- fields[1] ## We return the values print(paste0("sensor ",fields[1]," ok")) return( x ) }else{ print(paste0("Sensor ", fields[1] ," not selected")) r = try(nextElem(iter) )} } }# end while loop } -- L'absence de virus dans ce courrier électronique a été vérifiée par le logiciel antivirus Avast. https://www.avast.com/antivirus [[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.
