Get array elements from index to end

Question

Suppose we have the following array:

import numpy as np
a = np.arange(1, 10)
a = a.reshape(len(a), 1)
array([[1],
       [2],
       [3],
       [4],
       [5],
       [6],
       [7],
       [8],
       [9]])

Now, i want to access the elements from index 4 to the end:

a[3:-1]
array([[4],
       [5],
       [6],
       [7],
       [8]])

When i do this, the resulting vector is missing the last element, now there are five elements instead of six, why does it happen, and how can i get the last element without appending it?

Expected output:

array([[4],
       [5],
       [6],
       [7],
       [8],
       [9]])

Glorfindel · Accepted Answer · 2023-01-03 21:00:22Z

70

The [:-1] removes the last element. Instead of

a[3:-1]

write

a[3:]

You can read up on Python slicing notation here: Understanding slicing

NumPy slicing is an extension of that. The NumPy tutorial has some coverage: Indexing, Slicing and Iterating.

edited Jan 3, 2023 at 21:00

Glorfindel

22.8k13 gold badges97 silver badges124 bronze badges

answered Dec 5, 2012 at 20:46

NPE

503k114 gold badges970 silver badges1k bronze badges

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

4 Comments

Edgar Andrés Margffoy Tuay Over a year ago

That worked indeed, thanks, i'm trying to convert some matlab code to python/numpy, and that reference guide NumPy fot Matlab users misses some important issues as indexing and slicing.

NPE Over a year ago

@Andfoy: I'd recommend reading the NumPy tutorial I linked to. It's not perfect, but should be a good start.

Brian Over a year ago

Is there an object or other "index" that can go where the -1 is to make it behave like a[3:]? I often find it would simplify the code I write..

Brian Over a year ago

I found the answer--use None--like a[3:None].

Collectives™ on Stack Overflow

Get array elements from index to end

1 Answer 1

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related