Inserting elements of one list into another list in Python

Question

I have two lists J1 and Leftover. I want to insert elements of Leftover into J1 at locations of 0 elements of J1 and ensure that new J1 has all non-zero elements in ascending order. I want the length of old and new J1[0] to be the same. I present the current and expected outputs.

import numpy as np
J1 = [[0, 2, 0, 0, 0, 9, 0]]
Leftover=[1,4]

for i in range(0,len(Leftover)): 
    J1.insert(Leftover[i],i) 
print("J1 =",J1)

The current output is

J1 = [[0, 2, 0, 0, 0, 9, 0], 0, 1]

The expected output is

J1 = [[1, 2, 4, 0, 0, 9, 0]]

Asked By: bekarhunmain

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Source

Answer 1

This code sorts even elements that are 0.

J1 = [[0, 2, 0, 0, 0, 9, 0]]
Leftover=[1,4]
J1[0].extend(Leftover)
J1[0].sort()
# J1:
# [[0, 0, 0, 0, 0, 1, 2, 4, 9]]

Since J1 is a list with a single list inside, you need to add new elements to J1[0] instead of J1.

Note that the solution doesn’t require numpy.

To replace elements that are 0 (instead of lengthening the list), do this:

J1 = [[0, 2, 0, 0, 0, 9, 0]]
Leftover=[1,4]

for lftovr in Leftover:
    for i in range(len(J1[0])):
        if J1[0][i] == 0:
            J1[0][i] = lftovr
            break
# J1:
# [[1, 2, 4, 0, 0, 9, 0]]

J1[0].sort()
# J1:
# [[0, 0, 0, 1, 2, 4, 9]]

Note that sorting elements without rearranging the 0s is an underspecified task from your post’s description: What if the original list is something like [3, 1, 0, 4, 0, 0, 9] and you would like to insert 2 and 5? To get something like [1, 2, 3, 4, 5, 0, 9], we would need to rearrange the original order of the items; pure replacement of 0s can’t do the job. But if we sort, we might as well sort the whole list (including the 0s).

Some assumptions you might be making that would make the problem better-defined:

the original list’s non-0 elements are already in sorted order
the required insertions can be done without rearranging any of the initial non-0 elements
there is enough space in the list

Answered By: Lover of Structure

Answer 2

If you want to insert Leftover in first element of J1 and sort first element of J1 in ascending order. Then the code will be:

J1 = [[0, 2, 0, 0, 0, 9, 0]]
Leftover=[1,4]
J1[0].extend(Leftover)
J1[0].sort()
print("J1 =", J1)

Output will be: J1 = [[0, 0, 0, 0, 0, 1, 2, 4, 9]]

Answered By: Masud Dipu

Inserting elements of one list into another list in Python

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