SAS关于宏、宏函数、宏变量、data步、proc步和call execute的理解
SAS宏和宏函数的问题困扰了我三年之久，终于在昨日想通了，而想通的原因也很搞笑，仅仅是当时意识到了sas宏和宏函数是两个东西，自定的宏并不是宏函数（在其他编程语言中自定义函数和语言本身函数是一样的，受此影响！）
转载请注明出处：http://www.cnblogs.com/SSSR/p/6380957.html
结论：sas宏并不具备sas宏函数的功能，它仅仅只是一段文本，这段文本中如果有参数和宏函数，我们只是把参数替换掉和宏函数执行了，然后生成一个正常的文本（包含data步和proc步）提交给sas运行。
遇到宏函数时会直接执行，遇到宏时会直接进行文本替换（宏中的宏函数也会直接执行），宏函数返回的文本会和其他的data步和proc步组合然后一起提交给sas步运行。
宏函数直接执行，sas函数需要在data步中执行（%put和put的区别）
下面来看两个简单的例子：
options symbolgen mprint;*将宏编译的过程也打印出来，以便进行测试;
%macro s(i);
%put &i.;
%mend;
data _null_;
set sashelp.class;
put name;
%s('program');
run;
/*以下是结果：汉字为注释
105 %macro s(i);
106
107 %put &i.;
108 %mend;
109
110 data _null_;
111 set sashelp.class;
112 put name;
113 %s('program'); //下面是这句宏调用的解析
SYMBOLGEN: Macro variable I resolves to 'program' // I是%s的宏参数，被替换成了program。下面是直接打印了program，这个是为啥呢？就是因为%put是宏函数，会立即执行，从而先打印了program，然后才会将正常的data步提交给sas执行，run;后的部分是宏编译完以后执行的结果。
'program'
114 run;
Alfred
Alice
Barbara
Carol
Henry
James
Jane
Janet
Jeffrey
John
Joyce
Judy
Louise
Mary
Philip
Robert
Ronald
Thomas
William
NOTE: There were 19 observations read from the data set SASHELP.CLASS.
NOTE: DATA statement used (Total process time):
real time 0.01 seconds
*/
%macro t(i);
put &i.;
%mend;
data _null_;
set sashelp.class;
%t(name);
%s('programe')
run;
/*以下为结果：中文为注释
135 %macro t(i);
136
137 put &i.;
138 %mend;
139
140 data _null_;
141 set sashelp.class;
142 %t(name);
SYMBOLGEN: Macro variable I resolves to name //宏变量I被解析成name，注意这个name不带双引号，
MPRINT(T): put name; //这里put name和data set等一起被提交给sas执行
143 %s('programe')
SYMBOLGEN: Macro variable I resolves to 'programe' //这个因为是%put所以被直接执行了。
'programe'
144 run;
Alfred
Alice
Barbara
Carol
Henry
James
Jane
Janet
Jeffrey
John
Joyce
Judy
Louise
Mary
Philip
Robert
Ronald
Thomas
William
NOTE: There were 19 observations read from the data set SASHELP.CLASS.
NOTE: DATA statement used (Total process time):
real time 0.00 seconds
cpu time 0.00 seconds
*/
proc print data=sashelp.class;
run;
再来看一个复杂的例子：
options symbolgen mprint;
data b;
input a1 a2 a3;
cards;
1 2 3
;
run;
%macro varx;
%do i=0 %to 2;
proc sql ;
select a%eval(&i.+1) into:a%eval(&i.+1)
from b;
quit;
%let j=%eval(&i.+1);
data _null_;
a= &&a&j.;
put a;
run;
%end ;
%mend varx;
%varx;
/*以下为结果：中文为注释，整个程序循环了三次i=0 1 2,所以会生成三次proc sql和三次data步，然后提交给sas运行。从这个就可以看出sas宏的一个作用，减少代码量，将重复的代码进行封装。
145 data b;
146 input a1 a2 a3;
147 cards;
NOTE: The data set WORK.B has 1 observations and 3 variables.
NOTE: DATA statement used (Total process time):
real time 0.01 seconds
cpu time 0.01 seconds
149 ;
150 run; //以上为数据集生成
151
152 %macro varx;
153 %do i=0 %to 2;
154 proc sql ;
155 select a%eval(&i.+1) into:a%eval(&i.+1)
156 from b;
157 quit;
158 %let j=%eval(&i.+1);
159 data _null_;
160 a= &&a&j.;
161 put a;
162 run;
163 %end ;
164 %mend varx;
165 %varx;
MPRINT(VARX): proc sql ;
SYMBOLGEN: Macro variable I resolves to 0
SYMBOLGEN: Macro variable I resolves to 0
MPRINT(VARX): select a1 into:a1 from b;
MPRINT(VARX): quit; //从proc sql到这里就是宏varx编译生成的一段proc sql代码，这部分提交给sas运行。
NOTE: PROCEDURE SQL used (Total process time):
real time 0.00 seconds
cpu time 0.00 seconds
SYMBOLGEN: Macro variable I resolves to 0
MPRINT(VARX): data _null_;
SYMBOLGEN: && resolves to &.
SYMBOLGEN: Macro variable J resolves to 1
SYMBOLGEN: Macro variable A1 resolves to 1
MPRINT(VARX): a= 1;
MPRINT(VARX): put a;
MPRINT(VARX): run; //从data步到这一行是宏varx编译生成的第二段代码data步，这段代码中宏变量I被编译成了0，j直接被计算成了1.这段代码也同样展示了select into生成的宏变量在其他程序中调用的执行顺序。
1
NOTE: DATA statement used (Total process time):
real time 0.00 seconds
cpu time 0.00 seconds
MPRINT(VARX): proc sql ;
SYMBOLGEN: Macro variable I resolves to 1
SYMBOLGEN: Macro variable I resolves to 1
MPRINT(VARX): select a2 into:a2 from b;
MPRINT(VARX): quit; //重复proc sql
NOTE: PROCEDURE SQL used (Total process time):
real time 0.00 seconds
cpu time 0.00 seconds
SYMBOLGEN: Macro variable I resolves to 1
MPRINT(VARX): data _null_;
SYMBOLGEN: && resolves to &.
SYMBOLGEN: Macro variable J resolves to 2
SYMBOLGEN: Macro variable A2 resolves to 2
MPRINT(VARX): a= 2;
MPRINT(VARX): put a;
MPRINT(VARX): run; //重复data
2
NOTE: DATA statement used (Total process time):
real time 0.00 seconds
cpu time 0.00 seconds
MPRINT(VARX): proc sql ;
SYMBOLGEN: Macro variable I resolves to 2
SYMBOLGEN: Macro variable I resolves to 2
MPRINT(VARX): select a3 into:a3 from b;
MPRINT(VARX): quit; //重复proc sql
NOTE: PROCEDURE SQL used (Total process time):
real time 0.01 seconds
cpu time 0.01 seconds
SYMBOLGEN: Macro variable I resolves to 2
MPRINT(VARX): data _null_;
SYMBOLGEN: && resolves to &.
SYMBOLGEN: Macro variable J resolves to 3
SYMBOLGEN: Macro variable A3 resolves to 3
MPRINT(VARX): a= 3;
MPRINT(VARX): put a;
MPRINT(VARX): run; //重复data
3
NOTE: DATA statement used (Total process time):
real time 0.00 seconds
cpu time 0.00 seconds
*/
未完，后续预告call execute（http://bbs.pinggu.org/thread-2377205-1-1.html 此链接的讲解非常透彻，同时call excute可以调用宏，而且讲解了在使用宏和宏变量时单引号和双引号的处理）。
在Python和R语言中，有一个for循环的功能非常好用，但是在sas中没有类似的功能。鉴于sas data步中的pdv是一行一行的读取执行的，so可以结合call execute来实现for循环功能：
以下代码实现的功能是将三行数据生成三个数据集，数据集的名称是dataset列的值。
data a;
input A B dataset $;
datalines;
1 2 ds_1
6 7 ds_2a
2 3 ds_100c
;
run;
data _null_;
set a;
call execute('data ' ||dataset||';'||'set a (firstobs=' ||_n_|| ' obs=' || _n_ || ');run;' );
run;
/* or */
data _null_;
set a;
call execute('data ' || dataset || ';' || 'set a ; if dataset= "' || dataset || '"; run ;' );
run;
