Question

install.packages("plyr", repos="http://cran.us.r-project.org")

The downloaded binary packages are in
    /var/folders/bh/x038t1s943qftp7jzrnkg1vm0000gn/T//Rtmpa5E0hb/downloaded_packages

d <- data.frame(year = round(runif(10, 2000, 2005)), count = round(runif(10, 0, 10)))

library(plyr)
ddply(d, 'year', mutate, mu=mean(count), sigma=sd(count), cv=mu/sigma)

   year count       mu    sigma       cv
1  2001     4 2.333333 1.527525 1.527525
2  2001     1 2.333333 1.527525 1.527525
3  2001     2 2.333333 1.527525 1.527525
4  2003     6 4.250000 3.947573 1.076611
5  2003     9 4.250000 3.947573 1.076611
6  2003     1 4.250000 3.947573 1.076611
7  2003     1 4.250000 3.947573 1.076611
8  2004     3 5.000000 2.828427 1.767767
9  2004     7 5.000000 2.828427 1.767767
10 2005     2 2.000000       NA       NA

par(mfrow=c(2,(1+length(unique(d$year)))/2), mar = c(3,3,1,1), oma=c(3,3,0,0))
d_ply(d, 'year', transform, plot(count, main=unique(year), type='o'))