[#179] Filter with math.isnan() instead of is not np.nan

This lets us handle math.nan when aggregating threshold metrics results. It
keeps np.nan more contained to the code that actually cares about Pandas and
Numpy.

hlink/linking/model_exploration/link_step_train_test_models.py

@@ -658,14 +658,9 @@ def _capture_prediction_results(
             fn_count,
             tn_count,
         ) = _get_confusion_matrix(predictions, dep_var)
-        precision_raw = metrics_core.precision(tp_count, fp_count)
-        recall_raw = metrics_core.recall(tp_count, fn_count)
-        mcc_raw = metrics_core.mcc(tp_count, tn_count, fp_count, fn_count)
-
-        # Convert Python's math.nan to np.nan for numpy/pandas processing
-        precision = precision_raw if not math.isnan(precision_raw) else np.nan
-        recall = recall_raw if not math.isnan(recall_raw) else np.nan
-        mcc = mcc_raw if not math.isnan(mcc_raw) else np.nan
+        precision = metrics_core.precision(tp_count, fp_count)
+        recall = metrics_core.recall(tp_count, fn_count)
+        mcc = metrics_core.mcc(tp_count, tn_count, fp_count, fn_count)
 
         result = ThresholdTestResult(
             precision=precision,
@@ -813,11 +808,11 @@ def _aggregate_per_threshold_results(
 
     # Pull out columns to be aggregated
     precision_test = [
-        r.precision for r in prediction_results if r.precision is not np.nan
+        r.precision for r in prediction_results if not math.isnan(r.precision)
     ]
-    recall_test = [r.recall for r in prediction_results if r.recall is not np.nan]
-    pr_auc_test = [r.pr_auc for r in prediction_results if r.pr_auc is not np.nan]
-    mcc_test = [r.mcc for r in prediction_results if r.mcc is not np.nan]
+    recall_test = [r.recall for r in prediction_results if not math.isnan(r.recall)]
+    pr_auc_test = [r.pr_auc for r in prediction_results if not math.isnan(r.pr_auc)]
+    mcc_test = [r.mcc for r in prediction_results if not math.isnan(r.mcc)]
 
     # # variance requires at least two values
     precision_test_sd = (