datastep - SAS task. Need to pick records conditionally -

i have been given task solve, i'm quite new programming language. when flag 0, have pick next immediate record, provided flag variable has 3 or more consecutive records value 1. have been going @ hours. below datastep. please suggest.

data two; input usubjid visit flag; cards; 1001 1 1 1001 2 1 1001 3 0 1001 4 1 1001 5 1 1001 6 1 1002 1 1 1002 2 1 1002 3 0 1002 4 1 1002 5 1 1003 1 0 1003 2 1 1003 3 1 1003 4 1 1003 5 1 ; run; 

output be:-

usubjid visit flag 1001     4     1  1003     2     1 

this have tried far.

proc sort data = 2 ;         usubjid ;     run;   proc transpose data = 2 out = tran ;         usubjid ;         id visit ;var flag ; run; data b ;     set tran ;     if ( ( _1 = _2 ) , ( _1 = _3 ) ) or ( ( _2 = _3 ) , ( _2 = _4 ) ) or ( ( _3 = _4 ) , (     _3 = _5 ) ) or         ( ( _4 = _5 ) , ( _4 = _6 ) ) ; run; proc sort data = b ;     usubjid ; run; data c ;     merge ( in = ) b ( in = b ) ;     usubjid ;     if ;                                                                 run;                                                                                    

ok. deleted old answer didn't understand looking for.

data two; set two; n = _n_; run;  proc sort data=two; descending n ; run;  data two; set two; retain count  0; if flag     count = count + 1; else      count = 0; run;  proc sort data=two; n; run;  data 2 (drop=count n); set two;  if lag(flag) = 0 , count >=3; run; 

first, add row number variable.

then sort value in reverse order.

add variable counts number of consecutive records flag=1.

resort original order.

finally, subset down looking for.