[R] R lattice stripplot add median line to data

[Luigi Marongiu]

Dear all,
I am plotting data with lattice's stripplot. Is it possible to add a
median line to each cluster?
This is the working example:

```
Sample =  c("A0", "A0", "A0", "A3", "A3", "A3", "A7", "A7", "A7",
            "A9", "A9", "A9", "H1", "H1",
            "H1", "H2", "H2", "H2", "H3", "H3", "H3", "P1", "P1", "P1",
            "P2", "P2", "P2", "P3",
            "P3", "P3", "P4", "P4", "P4", "P5", "P5", "P5", "P7", "P7",
            "P7", "A0", "A0", "A0",
            "A3", "A3", "A3", "A7", "A7", "A7", "A9", "A9", "A9", "H1",
            "H1", "H1", "H2", "H2",
            "H2", "H3", "H3", "H3", "P1", "P1", "P1", "P2", "P2", "P2",
            "P3", "P3", "P3", "P4",
            "P4", "P4", "P5", "P5", "P5", "P7", "P7", "P7")
Group = rep(c("Normal", "Tumour",  "Metastasis" ), 26)
Taxon = c(rep("Microviridae", 39), rep("Caudovirales", 39))
Aboundance = c(0, 151,   3,   0, 102, 509,   4,   1, 277,   4,  87,   7,
               16,  13,  22,  47,  12,   1,
                5, 251,   4,   8,   4,   2,  14,   4,   2,  10,   4,   4,
               13,   1,   1,   5,   7,   2,   6,   6,   4,   1,   2,   1,
               2,   1,   2,   0,   0,   2,   0,   0,   1,   0,   0,   0,
               0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,
               0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0,   0)
df = data.frame(Sample, Group, Taxon, Aboundance,
                stringsAsFactors = FALSE)
library(lattice)
stripplot(
  Aboundance ~ Taxon|Group,
  df,
  groups = Taxon,
  scales=list(y=list(log=T)),
  pch=16,  cex = 1.5,
  ylab = expression(bold("Number of taxons")),
  jitter.data = TRUE,
  layout=c(3,1),
  col = "black",
  # colour panels differently
  par.settings=list(strip.background=list(col=c("darkorchid3",
                                                "darkolivegreen3", "brown3"))),
  strip = function(..., bg) {
    strip.default(...,
                  bg = trellis.par.get("strip.background")$col[which.packet()])
  },
  # add median bar
)
```

Thank you
-- 
Best regards,
Luigi