CODEWITHSUNDEEP
pythonnumpy
Chris Kenedy
Chris Kenedy

Reputation: 11

Determining if a specific, ordered vector is in a list/array

I am working on some molecular dynamics using Python, and the arrays tend to get pretty large. It would be helpful to have a quick check to see if certain vectors appear in the arrays. After searching for way to do this, I was surprised to see this question doesn't seem to come up. In particular, if I have something like

import numpy as np
y = [[1,2,3], [1,3,2]]
x = np.array([[1,2,3],[3,2,1],[2,3,1],[10,5,6]])

and I want to see if the specific vectors from y are present in x (not just the elements), how would I do so? Using something like

for i in  y:
    if i in x:
        print(i)

will simply return every y array vector that contains at least one element of i. Thoughts?

Upvotes: 1

Views: 92

Answers (3)

Paul Panzer
Paul Panzer

Reputation: 53089

The best strategy will depend on sizes and numbers. A quick solution is

[np.where(np.all(x==row, axis=-1))[0] for row in y]
# [array([0]), array([], dtype=int64)]

The result list gives for each row in y a possibly empty array of positions in x where the row occurs.

Upvotes: 0

Prune
Prune

Reputation: 77860

You don't explicitly give your expected output, but I infer that you want to see only [1, 2, 3] as the output from this program.

You get that output if you make x merely another list, rather than a NumPy array.

Upvotes: 0

ODiogoSilva
ODiogoSilva

Reputation: 2414

If you want to check if ALL vectors in y are present in the array, you could try:

import numpy as np
y = [[1,2,3], [1,3,2]]
x = np.array([[1,2,3],[3,2,1],[2,3,1],[10,5,6]])

all(True if i in x else False for i in y)
# True

Upvotes: 1

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