R help - Dec 2004 - 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
 
	[[alternative HTML version deleted]]

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
>  
> 	[[alternative HTML version deleted]]
> 
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