title: Multiple contour plots in the same plot
body: <p>I am new to R and trying to draw multiple 2D contour plots in the same plot. I  tried with the following code.</p>
  
  <pre><code>dat1 &lt;- structure(list(x1 = c(1:10), y1 = c(10:20)), .Names = c("x1", "y1"), class = "data.frame", row.names = c(NA,-21L))
  dat2 &lt;- structure(list(x2 = c(10:20), y2 = c(20:30)), .Names = c("x2", "y2"), class = "data.frame", row.names = c(NA,-21L))
  Contourcolors &lt;- colorRampPalette(c('yellow',"red"))(20)
  PointColors &lt;- c(rep('green',5),rep('blue',5))
  filled.contour(z=dat1,col=Contourcolors,
                 plot.axes=points( x=seq(0, 1, length.out = nrow(dat1)),
                                   y=rep(.5,20), 
                                   col=PointColors,cex=5,pch=19)
  )
  Error in as.matrix.data.frame(x) : 
    length of 'dimnames' [2] not equal to array extent
  </code></pre>
  
  <p>How can I do this easily with R?</p>