Nothing wrong with rolling your own, but see ?all.equal for R's built-in "almost.equal" version.
Bert Gunter Genentech Nonclinical Biostatistics -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Steve Lianoglou Sent: Monday, July 27, 2009 3:17 PM To: Mehdi Khan Cc: r-help@r-project.org Subject: Re: [R] Searching for specific values in a matrix Ahh .. On Jul 27, 2009, at 6:01 PM, Mehdi Khan wrote: > Even when choosing a value from the first few rows, it doesn't work. > okay here it goes: > > > rearranged[1:10, 1:5] > x y band1 VSCAT.001 soiltype > 1 -124.3949 40.42468 NA NA CD > 2 -124.3463 40.27358 NA NA CD > 3 -124.3357 40.25226 NA NA CD > 4 -124.3663 40.40241 NA NA CD > 5 -124.3674 40.49810 NA NA CD > 6 -124.3083 40.24744 NA 464 <NA> > 7 -124.3017 40.31295 NA NA D > 8 -124.3375 40.47557 NA 464 <NA> > 9 -124.2511 40.11697 1 NA <NA> > 10 -124.2532 40.12640 1 NA <NA> > > > query<- rearranged$y== 40.42468 > > rearranged[query,] > [1] x y band1 VSCAT.001 soiltype > <0 rows> (or 0-length row.names) This isn't working because the numbers you see for y (40.42468) isn't precisely what that number is. As I mentioned before you should use an "almost.equals" type of search for this scenario. My "%~%" function isn't working in your session because that is a function I've defined myself. You can of course use it, you just have to define it in your workspace. Paste these lines into your workspace (or save them to a file and "source" that file into your workspace). ## === almost.equal functions ==== almost.equal <- function(x, y, tolerance=.Machine$double.eps^0.5) { abs(x - y) < tolerance } "%~%" <- function(x, y) almost.equal(x, y) ## === end paste ============== Now you can use %~% once that's in. Let's use the almost.equal function now because I don't know if the default tolerance here is too strict (I suspect showing the value for rearranged$y[1] will show you more significant digits than you're seeing in the table(?)) query <- almost.equal(rearranged$y, 40.42468, tolerance=0.0001) rearranged[query,] This will get you something. > query<- rearranged$ VSCAT.001== 464 > except it's a huge table (I guess I have to get rid of all rows > with NA). Yes, I believe I mentioned earlier that you have to axe the NA matches manually: query <- rearranged$VSCAT.001 == 464 & !is.na(rearranged$VSCAT.001) rearranged[query,] Will get you what you want. > I tried using the %~% but R doesn't recognize it. So maybe it has > to do with the rounding errors? Rounding errors won't happen with integer comparisons (and it looks like the VSCAT.001 columns is integers, no?). -steve -- Steve Lianoglou Graduate Student: Computational Systems Biology | Memorial Sloan-Kettering Cancer Center | Weill Medical College of Cornell University Contact Info: http://cbio.mskcc.org/~lianos/contact ______________________________________________ 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.