Modify example code for quick nan removal

Author: dcamron

core/numpy/numpy-intermediate.ipynb

@@ -111,7 +111,8 @@
    "cell_type": "code",
    "execution_count": null,
    "metadata": {
-    "scrolled": true
+    "scrolled": true,
+    "tags": []
    },
    "outputs": [],
    "source": [
@@ -302,8 +303,9 @@
     "\n",
     "# BONUS POINTS: Plot only the data where heat index is defined by\n",
     "# inverting the mask (using ~mask) and setting invalid values to np.nan\n",
-    "temp[~good_heat_index] = np.nan\n",
-    "plt.plot(temp, 'tab:red')"
+    "plot_temp = temp.copy()\n",
+    "plot_temp[~good_heat_index] = np.nan\n",
+    "plt.plot(plot_temp, 'tab:red')"
    ]
   },
   {
@@ -403,16 +405,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "There are other numpy arg functions that return indices for operating:"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {},
-   "outputs": [],
-   "source": [
-    "np.*arg*?"
+    "There are other numpy arg functions that return indices for operating; check out the [NumPy docs](https://numpy.org/doc/stable/reference/routines.sort.html) on sorting your arrays!"
    ]
   },
   {