Update 3. Get Only What You Need, and Fast.md

Author: ortizfram

Introduction to MongoDB in Python/3. Get Only What You Need, and Fast.md

@@ -137,7 +137,39 @@ The Nobel database is again available to you as db. We also pre-loaded a sample
 
 ---
 Complete the definition of all_laureates(prize). Within the body of the function:
-- [x] Sort the "laureates" list of the prize document according to the "surname" key.
-- [x] For each of the laureates in the sorted list, extract the "surname" field.
-- [x] The code for joining the last names into a single string is already written for you.
-- [x] Take a look at the console to make sure the output looks like what you'd expect!
+- [x] 1. Sort the "laureates" list of the prize document according to the "surname" key.
+- [x] 1. For each of the laureates in the sorted list, extract the "surname" field.
+- [x] 1. The code for joining the last names into a single string is already written for you.
+- [x] 1. Take a look at the console to make sure the output looks like what you'd expect!
+```py
+from operator import itemgetter
+
+def all_laureates(prize):  
+  # sort the laureates by surname
+  sorted_laureates = sorted(prize["laureates"], key=itemgetter("surname"))
+  
+  # extract surnames
+  surnames = [laureate['surname'] for laureate in sorted_laureates]
+  
+  # concatenate surnames separated with " and " 
+  all_names = " and ".join(surnames)
+  
+  return all_names
+
+# test the function on a sample doc
+print(all_laureates(sample_prize))
+```
+- [x] 2. Find the documents for the prizes in the physics category, sort them in chronological order (by "year", ascending), and only fetch the "year", "laureates.firstname", and "laureates.surname" fields.
+```py
+# find physics prizes, project year and first and last name, and sort by year
+docs = db.prizes.find(
+           filter= {"category": "physics"}, 
+           projection= ['year', 'laureates.firstname', 'laureates.surname'], 
+           sort= [('year', 1)])
+```
+- [x] 3. Now that you have the prizes, and the function to extract laureates from a prize, print the year and the names of the laureates (use your all_laureates() function) for each prize document.
+```py
+# print the year and laureate names (from all_laureates)
+for doc in docs:
+  print("{year}: {names}".format(year=doc['year'], names=all_laureates(doc)))
+```