R ggplot2，如何在值栏中绘制一条均值线？

Question

I have the following values that I want to plot into a bar chart with R ggplot2 :

chr1.0  41.744548
chr1.1  52.77
chr1.2  38.941655
chr1.3  34.448161
chr1.4  49.671
chr1.5  36.515152
chr1.6  87.289
chr1.7  52.401747
chr10.0 35.671642
chr10.1 45.259939
chr10.2 81.22807
chr11.0 27.639752
chr11.1 40.451128
chr11.2 32.051282
chr11.3 70.05
chr11.4 35.691824
chr11.5 78.409091
chr12.0 79.77707
chr12.1 73.921
chr12.2 81.6609
chr13.0 31.055901
chr13.1 66.818182
chr14.0 10.785824
chr15.0 26.8657
chr16.0 11.7161
chr16.1 87.5
chr17.0 18.56678
chr17.1     66.055
chr18.0 82.773109
chr19.0 17.453505
chr2.0  24.7734
chr2.1  47.2613
chr2.2  52.922591
chr2.3  56.661046
chr2.4  35
chr2.5  38.848921
chr20.0 41.157
chr20.1     39.712919
chr21.0 40.791738
chr22.0     25.406204
chr22.1 37.614679
chr3.0  46.141975
chr3.1  51.441578
chr3.2  13.875598
chr3.3  41.248097
chr3.4  41.810345
chr4.0  23.982558
chr4.1  85.598706
chr4.2  40.449438
chr4.3  38.028169
chr5.0  16.224189
chr5.1  51.482059
chr5.2  40.980736
chr5.3  46.693387
chr6.0  97.854785
chr6.1  62.947
chr6.2  24.276527
chr6.3  18.449198
chr7.0  17.567568
chr7.1  72.006221
chr7.2  76.049767
chr7.3  40.96
chr8.0  41.269841
chr8.1  61.185185
chr8.2  16.99
chr8.3  46.031746
chr9.0  64.723926
chr9.1  38.125
chr9.2  39.148073

I found the commands to do this:

mydata <- read.table("myfile.dat")
colnames(mydata) <- c("chromName", "precisionEUC");
ggplot(mydata, aes(x=chromName, y=precisionEUC)) + 
  geom_bar(aes(fill=precisionEUC>=50), colour="black", 
           position=position_dodge(), stat="identity") + 
  xlab("chromName [a-z]") + 
  ylab("precision LDA-Euclidean")

And that's what I got:

Among the bars, I also want to print an horizontal line that indicates the mean of the analyzed values, but I don't know how to do this. In my case the mean is 46.23%, and so I would like to know how to modify the previous R commands to print an horizontal line, to produce something like:

Any idea on how to do this? Thanks!

Answer 1

Modifying your earlier code:

ggplot(mydata, aes(x=chromName, y=precisionEUC)) + 
  geom_bar(aes(fill=precisionEUC>=50), colour="black", 
           position=position_dodge(), stat="identity") + 
  xlab("chromName [a-z]") + 
  ylab("precision LDA-Euclidean") +
  geom_hline(yintercept = mean(precisionEUC))