[R] add median/mean line to stri-plot in lattice

[Luigi Marongiu]

dear all,
I set a series of variable subdivided in classes (there are 7 in here,
defined by the clause 'levels'), and I am showing the results in strip
chart using the package 'lattice'. Whitin each class the samples are
further subdivided in "active" (A) and "latent" (L). The function I have
written is:

stripplot(my.data.IP10$ratio ~
factor(my.data.IP10$TB)|factor(my.data.IP10$stimulus,
   levels = c("ESAT6","CFP10","Rv3615c", "Rv2654", "Rv3879",
"Rv3873","PHA")),
   my.data, hor=F, layout = c(7,1), scales = list(relation = "same"),
   ylab=expression(bold("Ratio GOI/RG")), xlab=expression(bold("Antigen
stimulation")), main="IP10 expression", pch=19, col="black",
   par.settings = list(strip.background=list(col="white")),
   par.strip.text=list(font=2))

which defines the figure attached "IP10".
Providing the median or average values (that will depend on the
distribution of the final data), is there a way to add a line overlapping
each of these classes and subclasses? I reckon it will be a vector of 14
elements, which can be called "Mvect".
In addition is there a way to differently colour the subclasses? lest say
black for active and white for latent? I tried with 'group' but with not
success.

Thank you for any help, I am not quite familiar with the Latex codes. I am
also attaching the dataframe containing the data for further reference.
Best regards
Luigi
-------------- next part --------------
	patient	TB	gene	stimulus	ratio
1	A264	A	IP10	ESAT6	250.9
2	A264	A	IP10	CFP10	399.1
3	A264	A	IP10	Rv3615c	959.4
4	A264	A	IP10	Rv2654	1.994
5	A264	A	IP10	Rv3879	589.2
6	A264	A	IP10	Rv3873	5.366
7	A264	A	IP10	PHA	48.27
8	H041	L	IP10	ESAT6	10.32
9	H041	L	IP10	CFP10	 
10	H041	L	IP10	Rv3615c	3.33
11	H041	L	IP10	Rv2654	 
12	H041	L	IP10	Rv3879	1
13	H041	L	IP10	Rv3873	 
14	H041	L	IP10	PHA	1
15	A263	A	IP10	ESAT6	509.5
16	A263	A	IP10	CFP10	991
17	A263	A	IP10	Rv3615c	689.6
18	A263	A	IP10	Rv2654	1285
19	A263	A	IP10	Rv3879	683.7
20	A263	A	IP10	Rv3873	468.7
21	A263	A	IP10	PHA	47.08
22	N241	A	IP10	ESAT6	8.534
23	N241	A	IP10	CFP10	2.733
24	N241	A	IP10	Rv3615c	 
25	N241	A	IP10	Rv2654	11.18
26	N241	A	IP10	Rv3879	10.41
27	N241	A	IP10	Rv3873	0.7532
28	N241	A	IP10	PHA