01 commits <- read.csv("perl-git-log.csv")
02 
03 commits$year <- format(
04   as.POSIXlt(
05     commits$time, 
06     origin="1970-01-01"), 
07   "%Y"
08 )
09 
10 files.per.year <- table( commits$year )
11 
12 png(file="files-per-year.png")
13 plot( files.per.year, 
14       xlab="Year", ylab="Files Modified", type = "b" )