Select 'area' from a 2D array in python

Question

Is there a way to select a particular 'area' of a 2d array in python? I can use array slicing to project out only one row or column but I am unsure about how to pick a 'subarray' from the large 2d array. Thanks in advance Jack

Answer 1

If you are using the numpy library, you can use numpy's more advanced slicing to accomplish this like so:

import numpy as np
x = np.array([[1, 2, 3, 4], 
              [5, 6, 7, 8], 
              [9, 10, 11, 12]])

print x[0:2,  2:4]
#       ^^^   ^^^
#       rows  cols

# Result:
[[3 4]
 [7 8]]

(more info in the numpy docs)

If you don't want to use numpy, you can use a list comprehension like this:

x = [[1, 2, 3, 4], 
     [5, 6, 7, 8], 
     [9, 10, 11, 12]]

print [row[2:4] for row in x[0:2]]
#          ^^^      ^^^ select only rows of index 0 or 1
#          ^^^ and only columns of index 2 or 3

# Result:
[[3, 4], 
 [7, 8]]