fix cyfi445 lab 7

CYFI445/lectures/07_binary_classification_n_to_1/0_predict_breast_cancer_A_steps.ipynb

@@ -217,14 +217,20 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 11,
+   "execution_count": null,
    "id": "3aeb88da",
    "metadata": {},
    "outputs": [],
    "source": [
     "# Scale features\n",
     "scaler = StandardScaler()\n",
+    "# fit() computes the mean and std of each feature using the training data only.\n",
+    "# transform() applies the standardization formula to scale the data.\n",
+    "# fit_transform() does both in one step.\n",
     "X_train = scaler.fit_transform(X_train)\n",
+    "# Very important: we do not fit again on the test set.\n",
+    "# Instead, we use the same mean and std from the training set (stored inside scaler) to transform the test data.\n",
+    "# This prevents data leakage — making sure the test set stays “unseen” during training.\n",
     "X_test = scaler.transform(X_test)\n",
     "\n",
     "# Convert to PyTorch tensors\n",