Slicing 2D NumPy Array, removing first and last row and column

Question

I have a 2D Numpy array of tile objects that serves as a map. The outer ring is all "wall" values to make a closed border. I want to make a copy of the inner values to iterate over without touching the outer rows and columns. I'm trying:

inner_values = map.tiles[1:-1][1:-1]

to cut off the top and bottom rows and left and right columns. My map is 100*70, and this keeps giving me an array of shape (96, 70) when I want (98, 68). How can I use slices correctly to get my inner values? Thanks!

Tbe second indexing is applied to the result of map.tiles[1:-1]. The net slice is [2:-2]. Not what you want. — hpaulj
– hpaulj, Commented Jan 4, 2022 at 3:58
As a side note, don't use map as variable name. This is a (very useful) python builtin. — mozway
– mozway, Commented Jan 4, 2022 at 4:42

Mark · Accepted Answer · 2022-01-04 03:04:00Z

1

You are just about there...you can put all the indices inside the brackets to get what you want:

import numpy as np

a = np.ones([5, 5])
print(a)

# [[1. 1. 1. 1. 1.]
#  [1. 1. 1. 1. 1.]
#  [1. 1. 1. 1. 1.]
#  [1. 1. 1. 1. 1.]
#  [1. 1. 1. 1. 1.]]


a[1:-1, 1:-1] = 0
print(a)
# [[1. 1. 1. 1. 1.]
#  [1. 0. 0. 0. 1.]
#  [1. 0. 0. 0. 1.]
#  [1. 0. 0. 0. 1.]
#  [1. 1. 1. 1. 1.]]

Or given your dimensions:

a = np.ones([100,70])
a[1:-1, 1:-1].shape
# (98, 68)

answered Jan 4, 2022 at 3:04

Mark

92.7k8 gold badges116 silver badges156 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Slicing 2D NumPy Array, removing first and last row and column

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related