How to add a new column to a 2D Numpy array or matrix

Question

I have data and labels for a machine learning code. To save the data and labels in a TSV file, I want to add labels to the existing data as the last column. How can I do it?

E.g.

>>> x

array([[1, 2, 3],

       [4, 5, 6],

       [7, 8, 9]])

>>> y

array([0, 1, 2])

to

array([[1, 2, 3, 0],

       [4, 5, 6, 1],

       [7, 8, 9, 2]]) 

Answer 1

You need to first reshape the labels and then you can use the append() function to add the labels as the last column of the data.

Here is an example:

>>> x=np.array([[1,2,3],[4,5,6],[7,8,9]])
>>> x
array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]])
>>> y=np.array([0,1,2])
>>> y=y.reshape(3,1)
>>> data=np.append(x,y, axis=1)
>>> data
array([[1, 2, 3, 0],
       [4, 5, 6, 1],
       [7, 8, 9, 2]])