Locating index of one list with respect to another list in Python

Question

I have lists J1 and J2. I want to locate the index of elements of J2 with respect to J1. For example, J2[0]=2 and this occurs at J1[1]. Hence, the index should be 1. Similarly for other elements of J2. I present the current and expected outputs.

import numpy as np
J1=[[1, 2, 4, 6, 7, 9, 10]]
J2=[[2, 6, 7, 9, 10]]
Indices=[i for i in J2 and J1]
print(Indices)

The current output is

[[1, 2, 4, 6, 7, 9, 10]]

The expected output is

[[1,3,4,5,6]]

Asked By: isaacmodi123

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Source

Answer 1

You can use index() to find the position of an item in a list.

import numpy as np
J1=[[1, 2, 4, 6, 7, 9, 10]]
J2=[[2, 6, 7, 9, 10]]
Indices=[[J1[0].index(i) for i in J2[0]]]
print(Indices)

Output:

[[1, 3, 4, 5, 6]]

Answered By: Mattravel

Answer 2

You can use the index() method to find the index in J1 for each element in J2.

Here’s the correct code:

import numpy as np

J1 = [1, 2, 4, 6, 7, 9, 10]
J2 = [2, 6, 7, 9, 10]

Indices = [J1.index(elem) for elem in J2]

print(Indices)
# output: [1, 3, 4, 5, 6]

J1.index(elem) returns the index of elem in J1, and then loop iterates over each element in J2.

Answered By: Franfrancisco9

Locating index of one list with respect to another list in Python

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