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]]

Your code never uses B. How could you expect to print its values??? — Serge Ballesta
– Serge Ballesta, Commented Feb 13, 2023 at 7:51
That's right. I don't really know how to refer the order so as to print values from B. — rajunarlikar123
– rajunarlikar123, Commented Feb 13, 2023 at 7:54
but indices= [[0,4],[1,6]] contains slices of A, not indices — RomanPerekhrest
– RomanPerekhrest, Commented Feb 13, 2023 at 8:01
You can call whatever you like. Basically, I want to locate [0,4] from indices in A and print the corresponding value from B i.e. [9.16435586e-05]. Similarly, for [1,6]. — rajunarlikar123
– rajunarlikar123, Commented Feb 13, 2023 at 8:03

Talha Tayyab · Accepted Answer · 2023-02-13 08:12:57Z

1

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]]

edited Feb 13, 2023 at 8:12

answered Feb 13, 2023 at 8:06

Talha Tayyab

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1 Comment

rajunarlikar123 Over a year ago

Is there a way to append the B values?

Hazem Ahmed · Accepted Answer · 2023-02-13 08:04:25Z

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 Feb 13, 2023 at 8:04

Hazem Ahmed

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Comments

Serge Ballesta · Accepted Answer · 2023-02-13 08:07:40Z

1

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 Feb 13, 2023 at 8:07

Serge Ballesta

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beh aaron · Accepted Answer · 2023-02-13 08:08:21Z

1

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 Feb 13, 2023 at 8:08

beh aaron

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