Merge pull request #16543 from Genie-Liu/fix-metrics.Precision

fix fluid.metrics.Precision bug

python/paddle/fluid/metrics.py

@@ -241,9 +241,11 @@ class Precision(MetricBase):
             raise ValueError("The 'preds' must be a numpy ndarray.")
         if not _is_numpy_(labels):
             raise ValueError("The 'labels' must be a numpy ndarray.")
-        sample_num = labels[0]
+        sample_num = labels.shape[0]
+        preds = np.rint(preds).astype("int32")
+
         for i in range(sample_num):
-            pred = preds[i].astype("int32")
+            pred = preds[i]
             label = labels[i]
             if label == 1:
                 if pred == label: