How do you extract a column from a multi-dimensional array?

In Python, you can extract a column from a multi-dimensional array (e.g. a 2D numpy array) by indexing it using the column number. For example, if you have a 2D numpy array called arr, you can extract the i-th column by using the following code snippet:

column_i = arr[:, i]

Here the : is used to select all the rows, and i is the column number you want to extract.

You can also use the numpy function take to extract a column from a 2D numpy array. For example:

column_i = np.take(arr, i, axis=1)

Here i is the column number you want to extract, and axis=1 specifies that you want to extract a column (as opposed to a row, which would be axis=0).