centering and standardizing with scale()

Welcome to some handy functions! These are quick ways to get some common tasks done: centering, standardizing, and getting stats (i.e. mean) for each level of a factor.


# get some data to play with
data()
# Ooo! Chickens. Let's use the ChickWeight dataset.
df <- ChickWeight str(df) summary(df) head(df) # ------------------- # # centering # # ------------------- # ?scale df$weight.c <- scale(df$weight, center=TRUE, scale=FALSE) hist(df$weight.c) # ---------------------------- # # scaling (z scores) # # ---------------------------- # df$weight.z <- scale(df$weight, center=TRUE, scale=TRUE) hist(df$weight.z) # ----------------------------------- # # within levels of a factor # # ----------------------------------- # # lots of great ways to do this, here are two (there are so many more!) # strategy number 1 ?ave df$ave.weight <- ave(df$weight, df$Chick) head(df, n=15) # you don't have to stick with the mean. you can put in any function you like. df$max.weight <- ave(df$weight, df$Chick, FUN=max) # you can center within levels of a factor! df$weight.z.within <- ave(df$weight, df$Chick, FUN=scale) head(df, n=15) # strategy number 2 ?by hist(by(df$weight, df$Chick, FUN=mean), main = "How heavy are those chickens??") # note that this one produces only one mean for each chick: length(unique(df$Chick)) length(by(df$weight, df$Chick, FUN=mean)) nrow(df) # you can put in any function you like hist(by(df$weight, df$Chick, FUN=max), main = "What's the fattest those chickens get??")