From 999c2c4ad7b8225dbb06fc80b5c844bae2ea59ba Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Fri, 17 Jul 2026 17:39:42 +0000
Subject: [PATCH] Clarify missing height correlation example

---
 1-Introduction/04-stats-and-probability/notebook.ipynb | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/1-Introduction/04-stats-and-probability/notebook.ipynb b/1-Introduction/04-stats-and-probability/notebook.ipynb
index 47b39def..5b84120e 100644
--- a/1-Introduction/04-stats-and-probability/notebook.ipynb
+++ b/1-Introduction/04-stats-and-probability/notebook.ipynb
@@ -487,18 +487,18 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "np.corrcoef(df['Height'].ffill(),df['Weight'])"
+    "np.corrcoef(df['Height'], df['Weight'])"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "Unfortunately, we did not get any results - only some strange `nan` values. This is due to the fact that some of the values in our series are undefined, represented as `nan`, which causes the result of the operation to be undefined as well. By looking at the matrix we can see that `Weight` is the problematic column, because self-correlation between `Height` values has been computed.\n",
+    "Unfortunately, we did not get a correlation result—only `nan` values involving `Height`. This happens because `Height` contains a missing value, represented as `nan`, so calculations that use that column are also undefined. The `1` in the bottom-right of the matrix is the self-correlation of `Weight`, which has no missing values.\n",
     "\n",
     "> This example shows the importance of **data preparation** and **cleaning**. Without proper data we cannot compute anything.\n",
     "\n",
-    "Let's use `fillna` method to fill the missing values, and compute the correlation: "
+    "For this example, let's use `ffill` to replace the missing `Height` with the previous valid height, and then compute the correlation:"
    ]
   },
   {