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#  Section 9
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# Extracting subsets of a column

data(state)

tryit <- state.name[50:46]

tryit

match(tryit,state.name)

tryit %in% state.name

tryit2 <- c("Georgia", "Florida", "Guam")
tryit2 %in% state.name

state.name[-(31:40)]

#Extracting subsets of an array

bigmat<-matrix(1:100,nr=10,nc=10)

newmat <- bigmat[-1,]

newmat <- bigmat[,2:10]

newmat <- bigmat[1:3,1:3]

newmat <- bigmat[,c(2,8,6)]

tristate.region <- state.x77[c("South Carolina","Georgia", "North Carolina"),]

tristate.region

#Logical extraction

south.region <- state.x77[state.region=="South",]

south.region

my.logic <- state.x77[,2] > 5000

rich.states <- state.x77[my.logic,]

#Self-referential logical extraction
x=rnorm(10)
x[x>0]
x>0
which(x>0)
x[which(x>0)]

SouthHighIllit=state.x77[(state.region=="South")&(state.x77[,"Illiteracy"]>2.0),]
SouthHighIllit

#Ordering a variable

ord <- order(state.area)

ord

state.name[ord]

ord <- rev(order(state.area))

state.name[ord]

# Other ways to reverse ordering:

ord <- order(-state.area)

ord <- order(state.area, decreasing=TRUE)

#Ordering an entire array by a single column

Population <- state.x77[,"Population"]

ord <- rev(order(Population))

state.x77.popsorted <- state.x77[ord,]

state.x77.popsorted

#Shortcut:
state.x77.popsorted=state.x77[rev(order(state.x77[,"Population"])),]
state.x77.popsorted

#Ordering by two variables

state.dfr <- data.frame(state.name,state.region,state.x77)

ord <- order(as.character(state.region), (-Population))

state.dfr<-state.dfr[ord,]

state.dfr

# Simple sorting of a single vector:

Population

sort(Population)

sort(Population,decreasing=TRUE)