Removing specific elements from an array in Python

Question

I want to remove specific elements corresponding to certain indices of array inv_r. For example, I want to remove elements corresponding to indices (0,2),(1,0),(1,1) and obtain a flattened version as defined by T. The desired output is attached.

import numpy as np

inv_r=(1e4)*np.array([[0.60800941, 0.79907128, 0.99442121],
       [0.61174008, 0.84891968, 0.71449188],
       [0.6211801 , 0.88869614, 0.91835812]])

T=inv_r.flatten()
print([T])

The desired output is

[array([6080.0941, 7990.7128, 7144.9188,
       6211.801 , 8886.9614, 9183.5812])]

What about storing np.nan at those indexes, then flatten the array, while discaring nan values? — Itai Dagan
– Itai Dagan, Commented Jun 14, 2022 at 14:14

mozway · Accepted Answer · 2022-06-14 14:30:43Z

2

You can use numpy.ravel_multi_index to convert your 2D indices into a flatten index, then delete them from T:

idx = [(0,2),(1,0),(1,1)]

drop = np.ravel_multi_index(np.array(idx).T, dims=inv_r.shape)
# array([2, 3, 4])

T = np.delete(inv_r.flatten(), drop)

output:

array([6080.0941, 7990.7128, 7144.9188, 6211.801 , 8886.9614, 9183.5812])

answered Jun 14, 2022 at 14:30

mozway

267k13 gold badges56 silver badges106 bronze badges

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

2 Comments

Wiz123 Over a year ago

How will the code change if idx=[]? The output should be array([6080.0941, 7990.7128, 9944.2121,6117.4008, 8489.1968,7144.9188, 6211.801 , 8886.9614, 9183.5812]).

mozway Over a year ago

You can maybe use an if here: if empty list -> flatten only

Collectives™ on Stack Overflow

Removing specific elements from an array in Python

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related