X = np.column_stack()

This code snippet is incomplete as no arguments have been passed to the `column_stack()` function.

`np.column_stack()` is a NumPy function that takes a sequence of 1-D arrays and stacks them as columns to make a single 2-D array.

For example, if we have two arrays `a = [1, 2, 3]` and `b = [4, 5, 6]`, we can stack them horizontally as columns using `column_stack()`:

import numpy as np
a = np.array([1, 2, 3])
b = np.array([4, 5, 6])
X = np.column_stack((a, b)) # X is now [[1, 4], [2, 5], [3, 6]]