if last. 的意义

shiyiming

在SAS的Language Reference Concepts书中有一个例子(删节了部分数据)

data salaries;

input department $ name $ wagecategory $ wagerate;
cards;
bad carol salaried 20000
bad elizabeth salaried 5000
bad linda salaried 7000
bad thomas salaried 9000
bad lynne hourly 230
ddg jason hourly 200
ddg paul salaried 4000
ppd kevin salaried 5500
ppd amber hourly 150
ppd tina salaried 13000
;

data budget;
set salaries;
by department;
if wagecategory='salaried' then yearlywage=wagerate*12;
else if wagecategory='hourly' then yearlywage=wagerate*2000;

if first.department then payroll=0;
payroll+yearlywage;

if last.department;
run;

proc print;
run;

结果如下
Obs    department    payroll

  1        bad         952000
  2        ddg         448000
  3        ppd         522000

在data budget中的if last.department;语句起什么作用?

是不是与if last.department then output;一样?
前面if语句为什么不写入dataset?

shiyiming

表示该变量每个取值的最后一条记录。