Add weighted random strategy

backend/examples/assignment/strategies.py

@@ -0,0 +1,29 @@
+import abc
+import dataclasses
+from typing import List
+
+import numpy as np
+
+
+@dataclasses.dataclass
+class Assignment:
+    user: int
+    example: int
+
+
+class BaseStrategy(abc.ABC):
+    @abc.abstractmethod
+    def assign(self) -> List[Assignment]:
+        ...
+
+
+class WeightedRandomStrategy:
+    def __init__(self, dataset_size: int, weights: List[int]):
+        assert sum(weights) == 100
+        self.dataset_size = dataset_size
+        self.weights = weights
+
+    def assign(self) -> List[Assignment]:
+        proba = np.array(self.weights) / 100
+        assignees = np.random.choice(range(len(self.weights)), size=self.dataset_size, p=proba)
+        return [Assignment(user=user, example=example) for example, user in enumerate(assignees)]