Question

I have written a django query like this.

stud_record = Student.objects.filter()

Thus stud_record is a queryset.

Now what I want to do is, i want to calculate the total num of stud_record, and then divide it by 5.

For ex: I have 20 records in stud_record. After dividing by 5 I got 4 each. So now i want to rank the first four students as ran 1, then from 5-8 students as rank 2….16-20 students as rank 5. This rank will be inserted to the same stud_record and will be send to the template page.

How can we do it.

Currently I am getting the structure like this

[{'name': u'mark', 'roll': 71}, 
 {'name': u'robin', 'roll': 42}, 
 {'name': u'julien', 'roll': 39}]

After division and inserting the rank it should look like

[[{'name': u'mark', 'roll': 71, 'rank': 1}, 
  {'name': u'robin', 'roll': 42, 'rank': 1},] 
 [{'name': u'julien', 'roll': 39, 'rank': 2}]]

Right now I am getting 185 results in my stud_record. After dividing 185/5 i am getting 37 as result. Now i want to give rank 1 to 1-37 students, then rank 2 to 38-75 students… like this

Answer 1

Add ranks to your dicts first and then group them using itertools.groupby:

from itertools import groupby

lst = [{} for _ in range(21)]  # simple testlist

def rank_it(lst,n):
    for index,d in enumerate(lst):
        rank = index/(len(lst)/n)+1
        d['rank'] = rank if rank < n else n

rank_it(lst,5)  #  add ranks
[list(g) for _,g in groupby(lst, lambda x: x['rank'])]  #group by rank

out:

[[{'rank': 1}, {'rank': 1}, {'rank': 1}, {'rank': 1}],
 [{'rank': 2}, {'rank': 2}, {'rank': 2}, {'rank': 2}],
 [{'rank': 3}, {'rank': 3}, {'rank': 3}, {'rank': 3}],
 [{'rank': 4}, {'rank': 4}, {'rank': 4}, {'rank': 4}],
 [{'rank': 5}, {'rank': 5}, {'rank': 5}, {'rank': 5}, {'rank': 5}]]

NB! This solution needs the list to be sorted, if its not, add:
lst.sort(key=lambda x: x['roll'],reverse=True)