Ch1 friends examples.

.gitignore

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+.idea/
+env/
+tests/

README.md

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+# Data science from scratch
+
+Repo: https://github.com/joelgrus/data-science-from-scratch

ch1/friends.py

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+from typing import List, Dict, Tuple
+
+USERS = [
+    {"id": 0, "name": "Hero"},
+    {"id": 1, "name": "Dunn"},
+    {"id": 2, "name": "Sue"},
+    {"id": 3, "name": "Chi"},
+    {"id": 4, "name": "Thor"},
+    {"id": 5, "name": "Clive"},
+    {"id": 6, "name": "Hicks"},
+    {"id": 7, "name": "Devin"},
+    {"id": 8, "name": "Kate"},
+    {"id": 9, "name": "Klein"},
+
+]
+
+FRIENDSHIPS = [
+    (0, 1), (0, 2), (1, 2), (1, 3), (2, 3), (3, 4), (4, 5), (5, 6), (5, 7), (6, 8), (7, 8), (8, 9),
+]
+
+
+def add_friendships(users: List[Dict], friendships: List[Tuple[int, int]]) -> List[Dict]:
+    for user in users:
+        user['friends'] = []
+
+    for i, j in friendships:
+        users[i]["friends"].append(users[j])  # add j as friend of i
+        users[j]["friends"].append(users[i])  # add j as friend of i
+
+    return users
+
+
+def number_of_friends(user: Dict) -> int:
+    return len(user["friends"])
+
+
+def friend_counts(users: List[Dict]) -> List[Tuple[int, int]]:
+    """Returns a sorted list by number of friends"""
+    number_of_friends_by_id = [(user['id'], number_of_friends(user)) for user in users]
+
+    _sorted_list = sorted(number_of_friends_by_id,
+                          key=lambda tup: tup[1],
+                          reverse=True)
+    return _sorted_list
+
+
+if __name__ == "__main__":
+    users = add_friendships(USERS, FRIENDSHIPS)
+    total_connections = sum(number_of_friends(user) for user in users)
+    num_users = len(users)
+    avg_connections = total_connections / num_users
+    counts = friend_counts(users)
+
+    print(f"Total user count: {num_users}")
+    print(f"Total number of connections: {total_connections}")
+    print(f"Average connections: {avg_connections}")
+    print(counts)