Removing elements of one list with respect to another list in Python

Question

I have two lists A and B. I am removing element from A which is less than tol. But I also want to remove element from B corresponding to the removed element from A. For example, [[2.22105075e-18]] was removed from A. Corresponding to this, [[4,13]] should be removed from B. I present the current and expected output.

import numpy as np
A= [[9.16435586e-05], [0.000184193464], [9.28353239e-05], [2.22105075e-18]]
B= [[13, 14], [4, 5], [5, 14], [4, 13]]
tol=1e-12

CA=[[x[0]] for x in A if x[0]>tol]
CB=[x for x,y in enumerate(CA) if list(y) in B]
print(CB)

The current output is

[]

The expected output is

[[13, 14], [4, 5], [5, 14]]

Asked By: modishah123

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Source

Answer 1

You could process the two in parallel with zip:

CA, CB = map(list, zip(*((a, b) for a, b in zip(A, B) if a[0]>tol)))

# or
# CA, CB = map(list, zip(*(x for x in zip(A, B) if x[0][0]>tol)))

Output:

# CA
[[9.16435586e-05], [0.000184193464], [9.28353239e-05]]

# CB
[[13, 14], [4, 5], [5, 14]]

Answered By: mozway

Answer 2

The basic idea to achive your stated goal is as follows:

Pair up both lists A and B with zip to give pairs of the form (a, b).
Keep only the bs for meach a b pair which satisfy the predicate on a.

We can implement this several ways.

Comprehension implementation

A= [[9.16435586e-05], [0.000184193464], [9.28353239e-05], [2.22105075e-18]]                              
B= [[13, 14], [4, 5], [5, 14], [4, 13]]                                                                  
tol=1e-12                                                                                                
                                                                                                         
result = [b for a,b in zip(A, B) if a[0]>tol]

Explicit loop implementation

result = []                                                                                              
for i in range(len(A)):                                                                                  
    if A[i][0] > tol:                                                                                    
        result.append(B[i])

Both methods essentially implement the outlined algorithm.

Answered By: Xero Smith

Removing elements of one list with respect to another list in Python

Question:

Answers:

Comprehension implementation

Explicit loop implementation