Extracting first n columns of a numpy matrix

Question

I have an array like this:

  array([[-0.57098887, -0.4274751 , -0.38459931, -0.58593526],          [-0.22279713, -0.51723555,  0.82462029,  0.05319973],          [ 0.67492385, -0.69294472, -0.2531966 ,  0.01403201],          [ 0.41086611,  0.26374238,  0.32859738, -0.80848795]]) 

Now I want to extract the following:

   [-0.57098887, -0.4274751]    [-0.22279713, -0.51723555]    [ 0.67492385, -0.69294472]    [ 0.41086611,  0.26374238] 

So basically just first 2 columns..

Answer 1

If a is your array:

In [11]: a[:,:2] Out[11]:  array([[-0.57098887, -0.4274751 ],        [-0.22279713, -0.51723555],        [ 0.67492385, -0.69294472],        [ 0.41086611,  0.26374238]]) 

Answer 2

I know this is quite an old question -

A = [[1, 2, 3],      [4, 5, 6],      [7, 8, 9]] 

Let's say, you want to extract the first 2 rows and first 3 columns

A_NEW = A[0:2, 0:3] A_NEW = [[1, 2, 3],          [4, 5, 6]] 

Understanding the syntax

A_NEW = A[start_index_row : stop_index_row,            start_index_column : stop_index_column)] 

If one wants row 2 and column 2 and 3

A_NEW = A[1:2, 1:3] 

Reference the numpy indexing and slicing article - Indexing & Slicing