[R] Lattice, combine histogram and line graph

[Jim Burke]

Hello everyone,

I have a simple histogram of gasoline prices going back a few years that 
I want to insert a line graph of consumer price index (cpi) over the 
histogram.  I have looked through the "Lattice" book by Deepayan Sarkar 
but don't see anything there. How might this be done? An example would 
be wonderful.

Current code snippet follows. For example additional field to add as a 
line graph would be a cpi calculation like "gas_data$regular * (2010_cpi 
/ gas_data$year )".

xyplot( regular ~ as.Date(gas_data$dates,"%b %d, %Y") , data = gas_data,
        type = c("g", "h" ))

Thanks,
Jim Burke