plyr.r

#Fun stuff with plyr
#-------------------
#plyr .data, .variables to split on and .fun function applied
#understand the naming conventions of plyr with the first 2 letters
#e.g., ddply dd= split dataframe apply function out dataframe
#e.g., dlply dl = split dataframe apply function out list
#d = dataframe
#l = list
#a = array
#-------------------
#Groupwise Summaries
colnames(mtcars)
#[1] "mpg"  "cyl"  "disp" "hp"   "drat" "wt"   "qsec" "vs"   "am"   "gear" "carb"
library(plyr)
#highest mpg for cylinder type
ddply(mtcars, .(cyl), subset,  mpg == max(mpg))
#selcect out the highest 25% of mpg per cylinder 
ddply(mtcars, .(cyl), subset,  mpg > quantile(mpg, .75))