[R] selecting clusters of points

[Simon.Gatehouse@csiro.au]

Tony,
This may be of some help. I hope it is sufficiently self explanatory.  I
will be out of contact for a week so if you have any queries to response may
be a little slow.

****************************************************************************
********
function(xx, yy, nodes = locator(type = "l"))
{
##counts the number of lines in a polygon which cross a perpendicular
dropped below
##each point in xx,yy
## first strip points beyond max range of polygon nodes
        lenxmin <- length(nodes$x)
        wch <- c(lenxmin, 1)
        points(nodes$x[wch], nodes$y[wch], type = "l", lty = 1)
        xnr <- range(nodes$x)
        ynr <- range(nodes$y)
        indx <- seq(along = xx) 
        ## identify points within largest rectangle defined by nodes first
        isin <- xx > xnr[1] & xx < xnr[2] & yy > ynr[1] & yy < ynr[2]
        xx <- xx[isin]
        yy <- yy[isin]
        indx <- indx[isin]
        if(length(xx)) {
##put lines in form of slope and intercept coefficients
                xmin <- nodes$x
                ymin <- nodes$y
                xmax <- c(xmin[-1], xmin[1])
                ymax <- c(ymin[-1], ymin[1])
                dx <- xmin - xmax
                slope <- (ymin - ymax)/dx
                intercept <- (ymax * xmin - xmax * ymin)/dx
                lenrec <- length(xx)
                xmin <- matrix(xmin, ncol = lenxmin, nrow = lenrec, byrow =
T)
                xmax <- matrix(xmax, ncol = lenxmin, nrow = lenrec, byrow =
T)
                xint <- matrix(xx, ncol = lenxmin, nrow = lenrec, byrow = F)
                yint <- matrix(yy, ncol = lenxmin, nrow = lenrec, byrow = F)
                hint <- t(t(xint) * slope + intercept)
                yint <- hint <= yint & ((xint >= xmin & xint <= xmax) |
(xint <= 
                        xmin & xint >= xmax))
                isin[indx] <- is.odd(marsum(ifelse(yint, 1, 0)))
        }
        points(c(nodes$x, nodes$x[1]), c(nodes$y, nodes$y[1]), type = "l",
col
                 = 16, lty = 1)
        isin
}

****************************************************************************
*****************
Simon Gatehouse                                  
CSIRO Exploration and Mining,
Newbigin Close off Julius Ave
North Ryde, NSW
 
Mail:      PO Box 136, North Ryde
           NSW 1670, Australia
Phone:     61 (2) 9490 8677
Fax:       61 (2) 9490 8921
Mobile:    61  0407 130 635 
E-mail:    simon.gatehouse at csiro.au
Web Page:  http://www.csiro.au/


-----Original Message-----
From: Tony Long [mailto:tdlong at uci.edu]
Sent: Saturday, January 26, 2002 7:13 AM
To: r-help at stat.math.ethz.ch
Subject: [R] selecting clusters of points


All:

	Are there any functions out there for selecting all the 
points in a region of a plot.  I envision something like the 
identify() function except one could circle a cloud of points (and 
perhaps a vector would be returned of the same length as the points 
plotted indicating logical membership in the circled cloud).  Perhaps 
someone has done something with the locator() function that would 
allow this (or can suggest a way I could do this).   Thanks.  Tony
-- 

Tony Long

Ecology and Evolutionary Biology
Steinhaus Hall
University of California at Irvine
Irvine, CA
92697-2525

Tel:  (949) 824-2562   (office)
Tel:  (949) 824-5994   (lab)
Fax: (949) 824-2181

email:  tdlong at uci.edu
http://hjmuller.bio.uci.edu/~labhome/
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