Add weighted sequential strategy

backend/examples/assignment/strategies.py

@@ -18,6 +18,27 @@ class BaseStrategy(abc.ABC):
         ...
 
 
+class WeightedSequentialStrategy(BaseStrategy):
+    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]:
+        assignments = []
+        proba = np.array(self.weights) / 100
+        counts = np.round(proba * self.dataset_size).astype(int)
+        reminder = self.dataset_size - sum(counts)
+        for i in np.random.choice(range(len(self.weights)), size=reminder, p=proba):
+            counts[i] += 1
+
+        start = 0
+        for user, count in enumerate(counts):
+            assignments.extend([Assignment(user=user, example=example) for example in range(start, start + count)])
+            start += count
+        return assignments
+
+
 class WeightedRandomStrategy(BaseStrategy):
     def __init__(self, dataset_size: int, weights: List[int]):
         assert sum(weights) == 100