Re: [Rd] Lattice: Drawing a single contour line with a negative value fails

2009-08-22 Thread Deepayan Sarkar 
On 8/19/09, Thorn Thaler thot...@sbox.tugraz.at wrote:
 Hi everybody,

  I want to add a single contourline to a levelplot. While everything works
 fine if the value at which the line should be drawn is positive, there is an
 error if the value is negative:

  library(lattice)
  my.panel - function(..., at, contour=FALSE, labels=NULL) {
panel.levelplot(..., at=at, contour=contour, labels=labels)
panel.contourplot(..., contour=TRUE, labels=Contour, lwd=2,
   at=con)
  }

  x - y - 1:100
  df - expand.grid(x=x, y=y)
  df$z - apply(df, 1, function(x)
(x[1]^2+x[2]^2)*ifelse(x[1]^2+x[2]^2  5000, -1,1))
  col.regions - heat.colors(50)

  # Works
  con - 1000
  levelplot(df$z~df$x+df$y, col.regions=col.regions, panel=my.panel)

  # Does not work
  con - -1000
  levelplot(df$z~df$x+df$y, col.regions=col.regions, panel=my.panel)

  I've tracked down the error to the function cut.default, which takes an
 argument breaks, which should be either a numeric vector of two or more
 cut points or a single number (greater than or equal to 2) giving the number
 of intervals into which 'x' is to be cut.

  So it seems to me that a single contourline at a positive value works
 because the value is interpreted as the number of intervals, even though
 there is just this single line in the resulting plot.

  What would be the correct way to add just a single contour line to a
 levelplot, or is it indeed a bug?

Definitely a bug. It should be easy to fix (but I haven't had time to
get to it yet).

Using something like

con - c(-1000, NA)

seems to work though.

-Deepayan

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[Rd] Lattice: Drawing a single contour line with a negative value fails

2009-08-19 Thread Thorn Thaler 

Hi everybody,

I want to add a single contourline to a levelplot. While everything 
works fine if the value at which the line should be drawn is positive, 
there is an error if the value is negative:


library(lattice)
my.panel - function(..., at, contour=FALSE, labels=NULL) {
   panel.levelplot(..., at=at, contour=contour, labels=labels)
   panel.contourplot(..., contour=TRUE, labels=Contour, lwd=2,
  at=con)
}

x - y - 1:100
df - expand.grid(x=x, y=y)
df$z - apply(df, 1, function(x)
   (x[1]^2+x[2]^2)*ifelse(x[1]^2+x[2]^2  5000, -1,1))
col.regions - heat.colors(50)

# Works
con - 1000
levelplot(df$z~df$x+df$y, col.regions=col.regions, panel=my.panel)

# Does not work
con - -1000
levelplot(df$z~df$x+df$y, col.regions=col.regions, panel=my.panel)

I've tracked down the error to the function cut.default, which takes 
an argument breaks, which should be either a numeric vector of two or 
more cut points or a single number (greater than or equal to 2) giving 
the number of intervals into which 'x' is to be cut.


So it seems to me that a single contourline at a positive value works 
because the value is interpreted as the number of intervals, even though 
there is just this single line in the resulting plot.


What would be the correct way to add just a single contour line to a 
levelplot, or is it indeed a bug?


Thanks,

Thorn

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