Question

I have a problem with lists/arrays/matrix at Python.

I have a list of matrix (or arrays if it need to be) and i want to add to every single of of them a new column of ones (of the same number of lines). How can I do this??

I’ve a couple of things and didn’t get any success.

Thanks for the help.

Here’s an example:

>>> A=[mat([[1,2,3],[4,5,6],[7,8,9]]),mat([[1,0,0],[0,1,0],[0,0,1]])]
>>> A
[matrix([[1, 2, 3],
        [4, 5, 6],
        [7, 8, 9]]), matrix([[1, 0, 0],
        [0, 1, 0],
        [0, 0, 1]])]

Using the answer you guys told

>>> A = np.hstack((A, np.ones((A.shape[0],1),dtype=A.type)))

Traceback (most recent call last):
  File "<pyshell#14>", line 1, in <module>
    A = np.hstack((A, np.ones((A.shape[0],1),dtype=A.type)))
AttributeError: 'list' object has no attribute 'shape'`

Answer 1

Example for a 2D NumPy ndarray:

>>> m = np.arange(12).reshape(3,4)
>>> m = np.hstack((m, np.ones((m.shape[0], 1), dtype=m.dtype)))
>>> m
array([[ 0,  1,  2,  3,  1],
       [ 4,  5,  6,  7,  1],
       [ 8,  9, 10, 11,  1]])

Edit: It works the same for a matrix. For a list of matrices, you can use a for loop:

>>> matrices = [np.matrix(np.random.randn(3,4)) for i in range(10)]
>>> for i, m in enumerate(matrices):
...     matrices[i] = np.hstack((m, np.ones((m.shape[0], 1), dtype=m.dtype)))