cereal_read.table("cereal.txt",header=T)

cereal

attach(cereal)          # so we can use variable names

sodium
sort(sodium)            # ordered array
stem(sodium)            # stem and leaf plot
stem(sodium,scale=0.5)  # half as many rows
stem(sodium,scale=2)    # twice as many rows -- this is hard to read

x11()                   # open graphics window
hist(sodium)            # histogram
hist(sodium,breaks=4)   # histogram with fewer bins
hist(sodium,breaks=7)   # it ignores you here
hist(sodium,breaks=c(0,60,120,180,240,300,360))    # force the number of bins

par(mfrow=c(2,2))       # put four plots on one page
hist(sodium,breaks=4)
hist(sodium,breaks=c(0,70,140,210,280,350))
hist(sodium,breaks=c(0,60,120,180,240,300,360))
hist(sodium)

hist(sodium,breaks=c(0,70,140,210,280,350))
hist(sodium)
hist(sodium,breaks=12)
hist(sodium,breaks=23)

par(mfrow=c(1,1))       # go back to one plot per page
plot(sodium)            # plot in order they appear in the dataset
plot(sort(sodium))

plot(sugars,calories)   # scatterplot
hist(sugars)
hist(calories)
stem(calories)
stem(calories,scale=2)
plot(sodium, calories)

table(type)		# summary table
table(mfr)
table(mfr)/length(mfr)  # percentages
barplot(table(mfr))     # bar chart
pie(mfr)                # pie chart

table(shelf)
table(shelf,mfr)        # contingency (cross-tabulation) table
barplot(table(shelf,mfr),beside=T)   # side-by-side bar chart
table(shelf,mfr)/length(mfr)         # table of total percentages
round(100*table(shelf,mfr)/length(mfr),2)     # nicer display

# getting a table of row percentages is not easy -- one way:
round(t(100*apply(table(shelf,mfr),1,function(x){x/sum(x)})),2)
# another way:
row.sums_apply(table(shelf,mfr),1,sum)
round(100*sweep(table(shelf,mfr),1,row.sums,"/"),2)
# and here is a table of column percentages:
round(apply(table(shelf,mfr),2,function(x){x/sum(x)}),2)