[R] adding vertical segments to an xyplot in lattice

[Christopher W Ryan]

I have a dataframe that looks like this:

 > str(chr)
'data.frame':   84 obs. of  7 variables:
 $ county: Factor w/ 3 levels "Broome","Nassau",..: 3 3 3 3 3 3 3 3 3 3 ...
 $ item  : Factor w/ 28 levels "Access to healthy foods",..: 21 19 20
18 16 3 2 6 17 8 ...
 $ value : num  8644 15 3.5 3.9 7.7 ...
 $ low   : num  7897 9 2.5 2.6 7 ...
 $ high  : num  9390 22 4.5 5.2 8.4 37 30 23 24 101 ...
 $ target: num  5034 11 2.7 2.6 6.1 ...
 $ nys   : num  6099 16 3.5 3.3 8 ...

> head(chr)
    county                      item  value    low   high target    nys
1 Sullivan           Premature death 8644.0 7897.0 9390.0 5034.0 6099.0
2 Sullivan       Poor or fair health   15.0    9.0   22.0   11.0   16.0
3 Sullivan Poor physical health days    3.5    2.5    4.5    2.7    3.5
4 Sullivan   Poor mental health days    3.9    2.6    5.2    2.6    3.3
5 Sullivan           Low birthweight    7.7    7.0    8.4    6.1    8.0
6 Sullivan             Adult smoking   29.0   22.0   37.0   15.0   20.0

I'd like to graph high and low for "Premature death" for each of the
three counties, with 3 vertical line segments, one connecting those
two points for each county.  I can get the two points for each county:

>xyplot(low+high ~ county, data=subset(chr, item=="Premature death"))

but I have not yet been able to figure out how to draw the 3 vertical
line segments. Been struggling to understand panel functions, but no
success so far. I'd be grateful for any advice.

Thanks.

--Chris Ryan
SUNY Upstate Medical University
Clinical Campus at Binghamton