Ahh... Well than the key will be teacher, and the value will simply be <-1 * # students, class_id> .
Then, you will see in the reducer that the first 3 entries will always be the ones you wanted. On Mon, Apr 23, 2012 at 10:17 PM, Lac Trung <trungnb3...@gmail.com> wrote: > Hi Jay ! > I think it's a bit difference here. I want to get 30 classId for each > teacherId that have most students. > For example : get 3 classId. > (File1) > 1) Teacher1, Class11, 30 > 2) Teacher1, Class12, 29 > 3) Teacher1, Class13, 28 > 4) Teacher1, Class14, 27 > ... n ... > > n+1) Teacher2, Class21, 45 > n+2) Teacher2, Class22, 44 > n+3) Teacher2, Class23, 43 > n+4) Teacher2, Class24, 42 > ... n+m ... > > => return 3 line 1, 2, 3 for Teacher1 and line n+1, n+2, n+3 for Teacher2 > > > Vào 09:52 Ngày 24 tháng 4 năm 2012, Jay Vyas <jayunit...@gmail.com> đã > viết: > > > Its somewhat tricky to understand exactly what you need from your > > explanation, but I believe you want teachers who have the most students > in > > a given class. So for English, i have 10 teachers teaching the class - > and > > i want the ones with the highes # of students. > > > > You can output key= <classid>, value=<-1*#ofstudent,teacherid> as the > > values. > > > > The values will then be sorted, by # of students. You can thus pick > > teacher in the the first value of your reducer, and that will be the > > teacher for class id = xyz , with the highes number of students. > > > > You can also be smart in your mapper by running a combiner to remove the > > teacherids who are clearly not maximal. > > > > On Mon, Apr 23, 2012 at 9:38 PM, Lac Trung <trungnb3...@gmail.com> > wrote: > > > > > Hello everyone ! > > > > > > I have a problem with MapReduce [:(] like that : > > > I have 4 file input with 3 fields : teacherId, classId, numberOfStudent > > > (numberOfStudent is ordered by desc for each teach) > > > Output is top 30 classId that numberOfStudent is max for each teacher. > > > My approach is MapReduce like Wordcount example. But I don't know how > to > > > determine key for map function. > > > I run Wordcount example, understand its code but I have no experience > at > > > programming MapReduce. > > > > > > Can anyone help me to resolve this problem ? > > > Thanks so much ! > > > > > > > > > -- > > > Lạc Trung > > > 20083535 > > > > > > > > > > > -- > > Jay Vyas > > MMSB/UCHC > > > > > > -- > Lạc Trung > 20083535 > -- Jay Vyas MMSB/UCHC
