subset bug?

The subset() Help file says

"The select argument exists only for the method for data frames ..."

So if mat is a matrix and not a data.frame, this might be the source of 
your
problems.

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA

"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Mike Saunders
Sent: Friday, December 10, 2004 5:02 AM
To: R Help
Subject: [R] subset bug?

I ran into a problem with "subset" while working at home that
I am not sure is a bug or not.  I defined a custom function
to take a data frame of tree positions, sizes, and types
(containing the columns TRT, COMP, PLOT, X, Y, DBH and CON)
and wanted to make a stem map of the plot using different
symbols and colors to represent the different types of tree
stems.  I copied a bit of the code below, the part that gave
me troubles:

if(dim(subset(mat,CON==1 & DBH>11.43))[1]>0)
symbols(mat[mat$CON==1 &     mat$DBH>11.43,]$X,mat[mat$CON==1
& mat$DBH>11.43,]$Y,circles=log(mat[mat$CON==1 &
mat$DBH>11.43,]$DBH)*tuner,inches=FALSE,add=TRUE,fg="gray",lwd=2)

if(dim(subset(mat,CON==0 & DBH>11.43))[1]>0)
symbols(mat[mat$CON==0 & mat$DBH>11.43,]$X,mat[mat$CON==0 &
mat$DBH>11.43,]$Y,squares=log(mat[mat$CON==0 &
mat$DBH>11.43,]$DBH)*sqrt(pi)*tuner,inches=FALSE,add=TRUE,fg="
gray",lwd=2)

if(dim(subset(mat,CON==1 & DBH<=11.43))[1]>0)
symbols(mat[mat$CON==1 & mat$DBH<=11.43,]$X,mat[mat$CON==1 &
mat$DBH<=11.43,]$Y,circles=log(mat[mat$CON==1 &
mat$DBH<=11.43,]$DBH)*tuner,inches=FALSE,add=TRUE,fg="black",lwd=2)

if(dim(subset(mat,CON==0 & DBH<=11.43))[1]>0)
symbols(mat[mat$CON==0 & mat$DBH<=11.43,]$X,mat[mat$CON==0 &
mat$DBH<=11.43,]$Y,squares=log(mat[mat$CON==0 &
mat$DBH<=11.43,]$DBH)*sqrt(pi)*tuner,inches=FALSE,add=TRUE,fg=
"black",lwd=2)

 The item "tuner" just scales the symbol size.  As you can
see, I was using two columns to define the type of symbol
(CON: square vs. circle) and color (DBH: gray vs. black).  I
had to use the "if" statements because some of the plots did
not contain all combinations of tree types.  This worked fine
in giving me my plots.

Okay, the question I had was why I couldn't use the "subset"
function within the "symbols" command.  I was going to use:

subset(mat,CON==0 & DBH<=11.43,select=c(X,Y))

as the first entry into the symbols command, but it kept
giving me errors saying "xy.coords" could not convert it.
However, if I used the "plot" function with "subset" trimming
the data frame externally, it worked fine to plot the point
positions.  However, the help for "plot" and "plot.default"
says "xy.coords" is used within that function.  What am I
missing here?

Mike Saunders
Research Assistant
University of Maine

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