用sas导入数据bb.csv，计算上证指数的每日百分比收益率。用宏函数完成：给定年份，计算出该年的平均收益率。

1. 使用SAS导入数据bb.csv：

DATA bb;
    INFILE "C:\bb.csv" DSD FIRSTOBS=2;
    INPUT Date :DATE9. Code $ Open Close High Low Volume;
RUN;

2. 计算上证指数的每日百分比收益率：

DATA bb;
    SET bb;
    RET = (Close - OPEN) / OPEN;
    FORMAT RET percent8.4;
RUN;

3. 宏函数计算特定年份的平均收益率：

%macro avg_return(year);
    DATA bb_&year.;
        SET bb;
        WHERE YEAR(Date) = &year.;
    RUN;

    PROC MEANS DATA=bb_&year.;
        VAR Ret;
        OUTPUT OUT=mean_return MEAN=avg_return;
    RUN;

    %PUT 年份&year.的平均收益率为%SYSFUNC(putn(&avg_return,percent8.4));
%mend;

%avg_return(2021);