Re: [R] Plotting symbols and colors based upon data values

From: Peter Ehlers <ehlers_at_ucalgary.ca>
Date: Mon, 14 Mar 2011 05:16:41 -0700

On 2011-03-13 18:46, David Winsemius wrote:
>
> On Mar 13, 2011, at 8:51 PM, Mark Linderman wrote:
>
>> David, thank you for your quick reply. I spent a few minutes
>> getting your
>> command to work with some sparse synthetic data, and then spent
>> several
>> hours trying to figure out why my data didn't work (at least for
>> symbols,
>> colors look okay). I have massaged my data to where it is practically
>> indistinguishable from the synthetic data - yet it still doesn't work.
>> Attached are the two data files that can be plotted as follows:
>>
>> broken = read.table("broken.table",header=TRUE)
>> works = read.table("works.table",header=TRUE)
>> xyplot(Y ~ X | A, data=works, pch=works$C , col=works$B)
>> xyplot(Y ~ X | A, data=broken, pch=broken$C , col=broken$B)
>
> I get the same problem and after experimenting for a while I think I
> can solve it by randomizing the order of the entries:
>
> > broken<- broken[sample(417), ]
>
> > xyplot(Y ~ X | A, data=broken, pch=broken$C, col=broken$B)
>
> Why xyplot should fail to properly assign pch values just because all
> "1"'s are at the beginning seems to me to be a bug.

The pch/col argument will just cycle through its elements successively for each point plotted, beginning again with the first element for each panel. So, if the first 92 elements (the largest group in broken$A has 92 cases) of broken$C are all 1s, then you'll never see any other symbol in any of the panels. Note also that none of the panels show any 'blue' points, since there are no "blue"s in the first 92 elements of broken$B. That this seems to be 'fixed' by randomizing the rows of the data frame is an illusion. The colours/symbols aren't correctly associated with the points.

The way to get the desired effect is to use col/pch in the panel function:

  broken$B <- as.character(broken$B)
  xyplot(Y ~ X | A, data = broken,
    panel = function(x=X, y=Y, subscripts){

      panel.xyplot(x, y,
                   col = broken$B[subscripts],
                   pch = broken$C[subscripts])
  })

where 'subscripts' pulls out the appropriate parts of the data frame according to the panel being plotted and the colour vector should be of type 'character'.

Peter Ehlers

>
> --
> David.
>
> After confirming the the problem recurs when re-order()-ed by broken
> $C, I am appending dput( ordered-broken) for others to experiment
>
> > dput(broken[order(broken$C), ])
> structure(list(rown = c(91L, 193L, 128L, 8L, 143L, 46L, 60L,
> 99L, 112L, 67L, 25L, 15L, 188L, 93L, 115L, 4L, 190L, 64L, 147L,

<snip>



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