[R] Calculating distances between points in a data frame?

[Sander Oom]

Hi Gabor,

Thanks for your suggestion. However when installing the package gregmisc, I 
get the following error:

 > local({a <- CRAN.packages()
+ install.packages(select.list(a[,1],,TRUE), .libPaths()[1], available=a)})
trying URL `http://cran.r-project.org/bin/windows/contrib/1.9/PACKAGES'
Content type `text/plain; charset=iso-8859-1' length 17940 bytes
opened URL
downloaded 17Kb

trying URL 
`http://cran.r-project.org/bin/windows/contrib/1.9/gregmisc_1.11.0.zip'
Error in download.file(url, destfile, method, mode = "wb") :
         cannot open URL 
`http://cran.r-project.org/bin/windows/contrib/1.9/gregmisc_1.11.0.zip'
In addition: Warning message:
cannot open: HTTP status was `404 Not Found'
 >

I was quite surprised as well! I tried different mirrors, but to no avail.

Maybe tomorrow,

Sander.


At 18:44 2004/05/31, you wrote:

>Try using running from the gregmisc package with pad = TRUE:
>
>
>require(gregmisc)
>XY <- data.frame(num = seq(0,10), X = seq(0,30,3), Y = seq(0, 40, 4) )
>DistXY <- function(idx) {
>    i <- idx[2]
>    with(XY, sqrt( (X[i]-X[i-1])^2 + (Y[i]-Y[i-1])^2 ) )
>}
>XY$Dist <- running( 1:nrow(XY), width=2, fun = DistXY, pad = TRUE )
>
>
>Sander Oom <slist <at> oomvanlieshout.net> writes:
>
>:
>: Dear list,
>:
>: I would like to calculate the distance between consecutive points in a data
>: frame. Of course the first point in the data frame does not have a point of
>: origin, and should get a value NA. I have tried two different loops, which
>: both result in error:
>:
>:  > num <- seq(0,10,1)
>:  > X <- seq(0,30,3)
>:  > Y <- seq(0,40,4)
>:  > XY <- data.frame(num, X, Y)
>:  > attach(XY)
>:  > summary(XY)
>:        num             X              Y
>:   Min.   : 0.0   Min.   : 0.0   Min.   : 0
>:   1st Qu.: 2.5   1st Qu.: 7.5   1st Qu.:10
>:   Median : 5.0   Median :15.0   Median :20
>:   Mean   : 5.0   Mean   :15.0   Mean   :20
>:   3rd Qu.: 7.5   3rd Qu.:22.5   3rd Qu.:30
>:   Max.   :10.0   Max.   :30.0   Max.   :40
>:  > plot(X,Y)
>:  > rngNum <- range(num)
>:  > for (i in rngNum){
>: +     XY$DistXY[i] <- sqrt( ((X[i]-X[i-1])^2) + ((Y[i]-Y[i-1])^2) )
>: + }
>: Error in "$<-.data.frame"(`*tmp*`, "DistXY", value = sqrt(((X[i] - X[i -  :
>:          replacement has 10 rows, data has 11
>:  > for (i in rngNum){
>: +     XY$DistXY2[i] <- ifelse(i=min(rngNum), NA, sqrt(((X[i]-X[i-1])^2) +
>: ((Y[i]-Y[i-1])^2)) )
>: + }
>: Error in ifelse(i = min(rngNum), NA, sqrt(((X[i] - X[i - 1])^2) + ((Y[i] 
>-  :
>:          unused argument(s) (i ...)
>:  > detach(XY)
>:  >
>:
>: Any suggestions much appreciated,
>:
>: Sander Oom.
>:
>: --------------------------------------------------------------
>: Dr. Sander P. Oom
>: Animal, Plant and Environmental Sciences
>: University of the Witwatersrand
>: Private Bag 3
>: Wits 2050
>: South Africa
>:
>: Tel (work)      +27 (0)11 717 64 04
>: Tel (home)      +27 (0)18 297 44 51
>: Fax             +27 (0)18 299 24 64
>:
>: Email   sander <at> oomvanlieshout.net
>: Web     www.oomvanlieshout.net/sander
>:
>: ______________________________________________
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>:
>
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