How to create a this Matrix by Numpy , and sort the matrix at second row?

Question

I want to create a matrix by Numpy as follow:

the first column composed by 0 and 1 , in this case , the value is not important the second column composed by integer , I want to sort my matrix by this column.

[[[1,1,1,1,1] , [3]],
 [[0,0,0,0,0] , [2]],
 [[1,1,1,1,1] , [5]]]

The question is: - How to create matrix like that? - After created , how to sort this matrix by second column

and get the answer as follow:

[ [[0,0,0,0,0] , [2]],
  [[1,1,1,1,1] , [3]],
  [[1,1,1,1,1] , [5]] ]

I'm fresh in numpy, I tried a lot but didn't succeeded, please help.

Answer 1

In the following, I used newlines to format this code for clarity by putting your matrix rows onto separate lines. This is NOT necessary, but I feel it helps show the content of each row (basically a list with five items and a list with one item).

When defining a numpy array, you can also define the datatype (dtype) with both a field name and the type of data stored in that field. Lists are considered an object type by numpy, so for each row, I assigned a field name to each item in the row ('x' and 'y') and I assigned a data type of object .

n = np.array([ ([1,1,1,1,1] , [3]), 
               ([0,0,0,0,0] , [2]), 
               ([0,0,0,0,0] , [5])], 
               dtype=[('x', object),('y', object)]

Numpy arrays all have a builtin method called .sort() that enables you to sort the rows. If you give it an order argument using the name of a field, it will sort by the field (ie that column). In this case, we sort by the 'y' field/column.

n.sort(order='y')