all right thank you!  this was big help.

On Tue, Jul 28, 2009 at 2:22 AM, Martin Maechler <maechler@stat.math.ethz.ch
> wrote:

> >>>>> "BertG" == Bert Gunter <gunter.berton@gene.com>
> >>>>>     on Mon, 27 Jul 2009 15:30:08 -0700 writes:
>
>    BertG> Nothing wrong with rolling your own, but see
>    BertG> ?all.equal for R's built-in "almost.equal" version.
>
> Yes, indeed!  Note that that needs a little extra care, as it
> either returns TRUE or a character vector.
> In sum, I'd strongly suggest you use
>
>  %~% <- function(x,y) isTRUE(all.equal(x,y))
>
> Martin Maechler, ETH Zurich and R Core Team
>
>    BertG> Bert Gunter Genentech Nonclinical Biostatistics
>
>    BertG> -----Original Message----- From:
>    BertG> r-help-bounces@r-project.org
>    BertG> [mailto:r-help-bounces@r-project.org] On Behalf Of
>    BertG> Steve Lianoglou Sent: Monday, July 27, 2009 3:17 PM
>    BertG> To: Mehdi Khan Cc: r-help@r-project.org Subject: Re:
>    BertG> [R] Searching for specific values in a matrix
>
>    BertG> Ahh ..
>
>    BertG> 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$y== 40.42468 > rearranged[query,]
>    >> [1] x y band1 VSCAT.001 soiltype <0 rows> (or 0-length
>    >> row.names)
>
>     BertG> This isn't working because the numbers you see for y
>    BertG> (40.42468) isn't precisely what that number is. As I
>    BertG> mentioned before you should use an "almost.equals"
>    BertG> type of search for this scenario. My "%~%" function
>    BertG> isn't working in your session because that is a
>    BertG> function I've defined myself. You can of course use
>    BertG> it, you just have to define it in your
>    BertG> workspace. Paste these lines into your workspace (or
>    BertG> save them to a file and "source" that file into your
>    BertG> workspace).
>
>    BertG> ## === almost.equal functions ====
>
>    BertG> almost.equal <- function(x, y,
>    BertG> tolerance=.Machine$double.eps^0.5) { abs(x - y) <
>    BertG> tolerance }
>
>    BertG> "%~%" <- function(x, y) almost.equal(x, y)
>
>    BertG> ## === end paste ==============
>
>    BertG> Now you can use %~% once that's in. Let's use the
>    BertG> almost.equal function now because I don't know if the
>    BertG> default tolerance here is too strict (I suspect
>    BertG> showing the value for rearranged$y[1] will show you
>    BertG> more significant digits than you're seeing in the
>    BertG> table(?))
>
>    BertG> query <- almost.equal(rearranged$y, 40.42468,
>    BertG> tolerance=0.0001) rearranged[query,]
>
>    BertG> 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).
>
>     BertG> Yes, I believe I mentioned earlier that you have to
>    BertG> axe the NA matches manually:
>
>    BertG> query <- rearranged$VSCAT.001 == 464 &
>    BertG> !is.na(rearranged$VSCAT.001) rearranged[query,]
>
>    BertG> 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?
>
>     BertG> Rounding errors won't happen with integer comparisons
>    BertG> (and it looks like the VSCAT.001 columns is integers,
>    BertG> no?).
>
>    BertG> -steve
>
>    BertG> -- Steve Lianoglou Graduate Student: Computational
>    BertG> Systems Biology | Memorial Sloan-Kettering Cancer
>    BertG> Center | Weill Medical College of Cornell University
>    BertG> Contact Info: http://cbio.mskcc.org/~lianos/contact<http://cbio.mskcc.org/%7Elianos/contact>
>
>    BertG> ______________________________________________
>    BertG> R-help@r-project.org mailing list
>    BertG> https://stat.ethz.ch/mailman/listinfo/r-help PLEASE
>    BertG> do read the posting guide
>    BertG> http://www.R-project.org/posting-guide.html and
>    BertG> provide commented, minimal, self-contained,
>    BertG> reproducible code.
>
>    BertG> ______________________________________________
>    BertG> R-help@r-project.org mailing list
>    BertG> https://stat.ethz.ch/mailman/listinfo/r-help PLEASE
>    BertG> do read the posting guide
>    BertG> http://www.R-project.org/posting-guide.html and
>    BertG> provide commented, minimal, self-contained,
>    BertG> reproducible code.
>

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