Locating list elements in an array in Python

Question

I have two arrays A and B. I have a list indices.

I want to locate each element of indices in A and print the corresponding values from B. I present the current and expected outputs.

import numpy as np

A=np.array([[ 0,  4],
       [ 0,  5],
       [1,6]])

B=np.array([[9.16435586e-05],
       [1.84193464e-14],
       [1.781909182e-5]])

indices= [[0,4],[1,6]]

for i in range(0,len(indices)):
    A=indices[i]
    print(A)

The current output is:

[0, 4]
[1, 6]

The expected output is:

[[0,4],[1,6]]
[[9.16435586e-05],[1.781909182e-5]]

Asked By: rajunarlikar123

||

Source

Answer 1

To generate a list based on index match I would do it like that, you can also modify this based on your use case

new_list = []
for i, elem in enumerate(A):
    if list(elem) in indices:
        new_list.append(B[i])

Answered By: Hazem Ahmed

Answer 2

common_index=[x for x,y in enumerate(A) if list(y) in indices]
#[0, 2]
lst=[]

for t in common_index:
    lst.append(list(B[t]))

#output
[[9.16435586e-05], [1.781909182e-05]]

Answered By: God Is One

Answer 3

Numpy is good at processing arrays of numbers in a vectorized way. Here, you would better use plain Python lists:

A = [[ 0,  4],
       [ 0,  5],
       [1,6]]
B = [[9.16435586e-05],
       [1.84193464e-14],
       [1.781909182e-5]]
indices= [[0,4],[1,6]]
print([A[i] for i,v in enumerate(A) if v in indices])
print([B[i] for i,v in enumerate(A) if v in indices])

gives as expected:

[[0, 4], [1, 6]]
[[9.16435586e-05], [1.781909182e-05]]

Answered By: Serge Ballesta

Answer 4

You can use numpy’s where method to achieve this:

import numpy as np

A=np.array([[ 0,  4],
       [ 0,  5],
       [1,6]])

B=np.array([[9.16435586e-05],
       [1.84193464e-14],
       [1.781909182e-5]])

indices= [[0,4],[1,6]]

for i in range(0,len(indices)):
    index = np.where(A == i)
    print(index)
    print(A[index])
    print(B[index])

Answered By: beh aaron

Locating list elements in an array in Python

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