The previous elegant solutions required the use of the gsubfn package. Nothing wrong with that, of course, but I'm always curious whether still relatively simple base R solutions can be found, as they are often (but not always!) much faster. And anyway, it seems to be in the spirit of your query to try such a solution. So here is one base R approach that I believe works. I'll break it up into 2 lines so you can see what's going on.
## Using your example... ## First replace everything but the number with spaces > z <- gsub("[^[:digit:]E.+-]"," ",input) > z [1] " " [2] " 1.3770E-03 3.4644E-07" [3] " 1.9412E-04 4.8840E-08" [4] "" [5] " " [6] " 1.3770E-03 3.4644E-07" [7] " 1.9412E-04 4.8840E-08" ## Now it can be scanned to a numeric via > z<-scan(textConnection(z),what=0) Read 8 items > z [1] 1.3770e-03 3.4644e-07 1.9412e-04 4.8840e-08 1.3770e-03 3.4644e-07 1.9412e-04 4.8840e-08 ######## I believe this strategy is reasonably general, but I haven't checked it carefully and would appreciate folks pointing out where it trips up (e.g. perhaps with NA's). Best, Bert Gunter Genentech Nonclinical Biostatistics -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of baptiste auguie Sent: Wednesday, November 18, 2009 3:57 AM To: r-help Subject: [R] parsing numeric values Dear list, I'm seeking advice to extract some numeric values from a log file created by an external program. Consider the following example, input <- readLines(textConnection( "some text <ax> = 1.3770E-03 <bx> = 3.4644E-07 <ay> = 1.9412E-04 <by> = 4.8840E-08 other text <aax> = 1.3770E-03 <bbx> = 3.4644E-07 <aay> = 1.9412E-04 <bby> = 4.8840E-08")) ## this is what I want results <- c(as.numeric(strsplit(grep("<ax>", input,val=T), " ")[[1]][8]), as.numeric(strsplit(grep("<ay>", input,val=T), " ")[[1]][8]), as.numeric(strsplit(grep("<aax>", input,val=T), " ")[[1]][9]), as.numeric(strsplit(grep("<aay>", input,val=T), " ")[[1]][9]) ) ## [1] 0.00137700 0.00019412 0.00137700 0.00019412 The use of strsplit is not ideal here as there is a different number of space characters in the lines containing <ax> and <aax> for instance (hence the indices 8 and 9 respectively). I tried to use gsubfn for a cleaner construct, strapply(input, "<ax> += +([0-9.]+)", c, simplify=rbind,combine=as.numeric) but I can't seem to find the correct regular expression to deal with the exponent. Any tips are welcome! Best regards, baptiste ______________________________________________ R-help@r-project.org mailing list 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 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.