Flip Every Alternate Row in 2-D array- Python

Question

I am a beginner to programming and was trying how to learn to flip every alternate row in my 2-D array(python)

For Example:

     `Input
    a=[[1,2,3,4,5],
    [10,9,8,7,6],
    [11,12,13,14,15],
    [20,19,18,17,16],
    [21,22,23,24,25],
    [30,29,28,27,26]]'

    Output
    a_f=[[1,2,3,4,5],
    [6,7,8,9,10],
    [11,12,13,14,15],
    [16,17,18,19,20],
    [21,22,23,24,25],
    [26,27,28,29,30]] `

I tried using flip function from python doc strings but it reversed the whole array. Also is it possible that a code can flip every alternate row without me needing to specify how many rows are there every time.

Are you allowed to use, say `numpy`, or must not use external modules at all? — Daweo, Mar 29 '22 at 14:26
Yes, i am trying to learn numpy and pandas. so yes i can use it — Ahraar Shareef Muqsit -, Mar 29 '22 at 14:27
Welcome to stackoverflow! You can answer you own question instead of just making a comment :-) see https://stackoverflow.com/help/self-answer — ilam engl, Mar 29 '22 at 15:22

score 0 · Accepted Answer · answered Mar 29 '22 at 14:29

0

I suggest you start using NumPy when working with arrays. Here is a small script that performs your task. It uses enumerate to index the rows, modulus (i % 2 == 1) to distinguish between odd and even rows and use the numpy indexing [::-1] to flip the rows:

import numpy as np

def flip_even_rows(a):
    for i, row in enumerate(a):
        if i % 2 == 1:
            a[i] = row[::-1]
    return a

a = [[1,2,3,4,5],
     [10,9,8,7,6],
     [11,12,13,14,15],
     [20,19,18,17,16],
     [21,22,23,24,25],
     [30,29,28,27,26]]

a = np.array(a)

print(flip_even_rows(a))

answered Mar 29 '22 at 14:29

Martin Gardfjell

158
6

Thanks a lot for your quick response. The code works as i intended it to be. I wanted to store the value returning from the function in a variable, say "a_f", how can i do that? – Ahraar Shareef Muqsit - Mar 29 '22 at 14:58
just a_f = flip_even_rows(a) – Martin Gardfjell Mar 29 '22 at 15:11

Flip Every Alternate Row in 2-D array- Python

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