R - attach() detach() search(), summaryBy(), aggregate(), stack() -2020/01/16

#attach() detach() search()

Sepal.Width
attach(iris)
search()
head(Sepal.Length)
detach(iris)
search()
Sepal.Width
#if you changed values in sepal with after use attach(), the changed values do not affect iris 

##index

#which() which.max() , which.min()

subset(iris,Species =="setosa")
which(iris$Species =="setosa")
which.max(iris$Sepal.Length)
which.min(iris$Sepal.Length)

##calculation by group

#aggregate(x,by,function) or aggregate(formula(y~x),data, function)

aggregate(Sepal.Length ~ Species, iris, mean)

tapply(iris$Sepal.Length, iris$Species, mean)
library(doBy)
summaryBy(Sepal.Length~ iris$Species, iris)

##Tidy Data

#stack() unstack()

x<-data.frame(a=c(3,2,9),b=c(5,3,2),c=c(4,5,7))
x
(xstacked <- stack(x))

summaryBy(values~ind, xstacked)
unstack(xstacked,values~ind)