🧮 NumPy: Why axis=0 and axis=1 Feel Backwards

You've probably seen:

np.mean(X, axis=0)

and wondered:

"Why does axis 0 mean columns?"

Think about what NumPy is doing.

📌 axis=0 means:

Collapse the rows.

So you move down each column and get one value per column.

📌 axis=1 means:

Collapse the columns.

So you move across each row and get one value per row.

For:

1  2  3
4  5  6

np.mean(X, axis=0)

gives:

[2.5, 3.5, 4.5]

On the other hand:

np.mean(X, axis=1)

gives:

[2, 5]

Don't memorize the numbers.

Just Remember: The axis you specify is the dimension that gets collapsed.

#NumPy