Hi R Users,
I was struggling to overlay two graphs created from the two different datasets using ggplot2.I could not overlay two figures. I wanted to plot second graph using second Y axis. but there was no provision. 
Furthermore, I could not join means of the box plots.
 
I tried this way but did not work. Any suggestions?
dat1<-structure(list(site = c(1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 
2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L), layer = structure(c(2L, 
2L, 2L, 1L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 
1L, 1L), .Label = c("bottom", "top"), class = "factor"), Present = c(120L, 
125L, 123L, 23L, 21L, 19L, 131L, 124L, 127L, 24L, 27L, 25L, 145L, 
143L, 184L, 29L, 14L, 17L, 38L)), .Names = c("site", "layer", 
"Present"), row.names = c(NA, 19L), class = "data.frame")
dat1
dat2<-structure(list(site = 1:3, present = c(-3L, 2L, 5L)), .Names = c("site", 
"present"), row.names = c(NA, 3L), class = "data.frame")
dat2
library("plyr")
library(ggplot2)
A<-ggplot(dat1, aes(x = factor(site), y = Present, colour = layer, fill=layer)) + 
    geom_boxplot(outlier.shape = 16, outlier.size = 1)  + theme_bw()+ ylim(0,185)
# Here I wanted to join the means of the boxplots among the sites, but I could not join it.
B<-ggplot(dat2, aes(x=factor(site),y= present, colour="blue") + 
     geom_line() + geom_point()) # wanted to plot it using second y axis. 
A+B
Thanks for your help.
KG
 
  		 	   		  
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