Dear R-helpers:
I am an entry-level R user and have a question related to overlaying a
barchart and and a xyplot using latticeExtra.
My problem is that when I overlay them I fail to align their x-axes.
I show my problem below through an example.

#the example data frame is provided below

       vec <-c(1,5.056656,0.5977967,0.06126587,0.08557778,
 2,4.601049,0.5995989,0.05002188,0.11410027,
 3,4.932008,0.5502283,0.06727938,0.12531825,
 4,4.763798,0.5499489,0.06473846,0.10752641,
 5,4.944967,0.5328129,0.05445327,0.13663951,
 6,5.063504,0.5267245,0.06477738,0.12380332,
 7,4.735251,0.5528205,0.06851714,0.12196075,
 8,5.141733,0.5304151,0.07965567,0.15123277,
 9,5.215678,0.5219224,0.06694207,0.16476356,
10,4.930439,0.5712519,0.08591549,0.09710933,
11,5.075990,0.5615573,0.05778996,0.15361845,
12,4.909847,0.5683740,0.08711699,0.11189277,
13,4.863164,0.5652511,0.07222227,0.12071060,
14,5.173818,0.5564918,0.09830620,0.11831926,
15,4.762325,0.5345888,0.08792658,0.11738642,
16,5.046225,0.5268459,0.09574746,0.13254236,
17,4.902188,0.5370394,0.07194955,0.13164327,
18,4.865935,0.5446562,0.06894994,0.12645103,
19,5.204060,0.5650887,0.06726925,0.09242551,
20,5.208138,0.5765187,0.09282935,0.11053842)

df<-as.data.frame( t(matrix(vec,nrow=5,ncol=20)))
names(df)<-c("group","outcome","proportion_1","proportion_2","proportion_3")

library(latticeExtra)
library(lattice)

#First generate barchart to plot the 3 proportions
prop.data <-subset(df,select=c(proportion_1,proportion_2,proportion_3))
prop.tab <- as.table(as.matrix(prop.data))
barchart.obj<-barchart(prop.tab, stack=TRUE, horizontal = FALSE)
#Second, generate the dots of outcome (I could have used type="l" but using
type="p" makes the
#misalignment of x-axis more obvious.
dot.outcome <- xyplot(outcome~group,df,type="p", col="blue")

#Last, overlay the two plots
barchart.obj+ as.layer(dot.outcome,style=2,axes=c("y"), outside=TRUE)
#Now, you should be able to see the x-axis of the two plots are not
matching.
#i.e., a dot is not at the center of its correspoding bar.

How can I fix this?

Your help will be highly appreciated. Many thanks in advance.

-Sean

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