将一个值分配给可引用的新数据，其中组的计数在特定的数字上。

Question

enrolments<-data.table(ID=c(100001, 100001, 100001, 100001, 100002,  
100002, 100002, 100002),
start_date=c("Jan-10","Jan-10","Jun-10","Jun-10", "Jan-10","Jan-11","Jan-11","Jun-11"),       
subject_code = c(1:8), 
status = c("Pass","Fail","Withdrawn","Pass","Pass","Pass","Pass","Pass"))

我有一个data.table注册与student_IDs，开始日期，主题代码，状态(通过，撤回，失败)。

ID start_date subject_code状态 1 100001 /10 1通行证 2 100001 1/10 2失败 3 100001 6月10日3撤回 4 100001 6月-10 4通过 5. 100002 /10/5通行证 6 100002 /11 6通行证 7 100002 /11 7通行证 6月8日100002 -11日8次传球

我想创建一个新列"first_subjects“，如果前两个主题的状态被撤回或失败，列= Y，否则为N

数据已经按学生和日期进行了排序。

Answer 1

你可以试试

 enrolments[, first_subjects:=c('N', 'Y')[any(status[1:2] %in% 
                         c('Fail', 'Withdrawn'))+1] , by=ID]

 enrolments
 #       ID start_date subject_code    status first_subjects
 #1: 100001     Jan-10            1      Pass              Y
 #2: 100001     Jan-10            2      Fail              Y
 #3: 100001     Jun-10            3 Withdrawn              Y
 #4: 100001     Jun-10            4      Pass              Y
 #5: 100002     Jan-10            5      Pass              N
 #6: 100002     Jan-11            6      Pass              N
 #7: 100002     Jan-11            7      Pass              N
 #8: 100002     Jun-11            8      Pass              N