[R] Different labels by panel in barchart

[Richard.Cotton at hsl.gov.uk]

Dear all,

I'm analysing a survey, and creating a barchart of the different responses 
for each question.  The questions are grouped according to a number of 
categories, so I'm using lattice to create a plot with each question in a 
category on it.  The problem is that the response set for different 
questions within the same category varies.  I want to be able to draw only 
the relevant bars, without spaces for nonrelevant reposnes.  An example 
may make it clearer:

testdf = data.frame(y=c(23,34,45, 56), x=factor(c("a", "a", "b", "c")), 
g=factor(c(1,2,1,2)))
barchart(y~x|g, data=testdf)

#In the first panel I would like two columns "a" and "b", positioned at 1 
and 2 respectively; in the second I would again like two columns at 1 and 
2, this time labelled "a" and "c".

barchart(y~x|g, data=testdf, scales=list(x=list(relation="free")), 
drop.unused.levels=TRUE)

#This is closer, but puts the columns in the wrong place in the second 
panel.

Regards,
Richie.

Mathematical Sciences Unit
HSL


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