标题: example using FIRST. and LAST. Variables [打印本页] 作者: shiyiming 时间: 2005-10-19 16:00 标题: example using FIRST. and LAST. Variables [code:1d5a8]************************************************;
*** File: FIRSTLAST.sas ***;
*** example using FIRST. and LAST. Variables ***;
************************************************;
** step 1: create data set with some **;
** repeat subjects (SID) **;
DATA TEMP1;
INPUT SID VISIT SCORE;
CARDS;
01 1 87
02 1 77
03 1 62
02 2 54
03 2 77
04 2 21
;
RUN;
** first sort by ID variable **;
PROC SORT DATA=TEMP1;
BY SID;
RUN;
** create subset with only 1 visit **;
DATA ONEVISIT;
SET TEMP1;
BY SID;
IF FIRST.SID AND LAST.SID; * selects only those with one
* visit;
RUN;
PROC PRINT DATA=ONEVISIT;
TITLE1 'SUBJECTS WITH ONLY ONE VISIT';
RUN;
** create subset with 2 visits **;
DATA TWOVISIT;
SET TEMP1;
BY SID;
IF FIRST.SID=0 or LAST.SID=0; * selects with two visits;
RUN;
PROC PRINT DATA=TWOVISIT;
TITLE1 'BOTH VISITS FOR SUBJECTS WITH 2 VISITS';
RUN;[/code:1d5a8]