Prestige <-
  read.table('http://math.uttyler.edu/nathan/classes/statistics/data/prestige.data',header=TRUE)

Prestige[1:10,]

boxplot(Prestige$income)
hist(Prestige$income)

Prestige$income[7:10]
Prestige$income[Prestige$income > 10000]
Prestige$income[Prestige$type == "prof"] # incomes for professionals
Prestige$income[Prestige$type == "wc"] # incomes for white collars
boxplot(Prestige$income[Prestige$type=="prof"],Prestige$income[Prestige$type=="wc"])

###### a helpful shortcut to typing:
attach(Prestige)

# the previous boxplot
boxplot(income[type=="prof"],income[type=="wc"])

###### when you're done, don't forget to
# detach(Prestige)

t.test(income[type=="prof"],income[type=="wc"])

#	Welch Two Sample t-test
#
#data:  income[type == "prof"] and income[type == "wc"] 
#t = 5.2202, df = 39.673, p-value = 5.977e-06
#alternative hypothesis: true difference in means is not equal to 0 
#95 percent confidence interval:
# 3374.411 7639.884 
#sample estimates:
#mean of x mean of y 
#10559.452  5052.304 
#
#### 95% ci for difference between prof and wc incomes is
#####   3374 to 7639

t.test(income[type=='wc'],income[type=='bc'])