Get character from multiple strings in sequence

Question

How do I take the first character from each string in a list, join them together, then the second character from each string, join them together, and so on - and eventually create one combined string?

eg. if I have strings like these:

homanif
eiesdnt
ltiwege
lsworar

I want the end result to be helloitsmeiwaswonderingafter

I put together a very hackneyed version of this which does the job but produces an extra line of gibberish. Considering this is prone to index going out of range, I don't think this is a good approach:

final_c = ['homanif', 'eiesdnt', 'ltiwege', 'lsworar']

final_message = ""
current_char = 0

for i in range(len(final_c[1])):
    for c in final_c:
        final_message += c[current_char]
    current_char += 1

final_message += final_c[0][:-1]    

print(final_message)

gives me helloitsmeiwaswonderingafterhomani when it should simply stop at helloitsmeiwaswonderingafter.

How do I improve this?

@Chris_Rands your solution worked great! I wish I could mark it as the answer. — Mayukh Nair
– Mayukh Nair, Commented Feb 13, 2019 at 13:29

Olivier Melançon · Accepted Answer · 2019-02-13 13:20:17Z

3

Problems related to iterating in some convoluted order can often be solved elegantly with itertools.

Using zip

You can use zip and itertools.chain together.

from itertools import chain

final_c = ['homanif', 'eiesdnt', 'ltiwege', 'lsworar']
final_message = ''.join(chain.from_iterable(zip(*final_c))) # 'helloitsmeiwaswonderingafter'

In the event you needed the strings in final_c to be of different lengths, you could tweak your code a bit by using itertools.zip_longest.

final_message = ''.join(filter(None, chain.from_iterable(zip_longest(*final_c))))

Using cycle

The fun part with itertools is that it offers plenty of clever short solutions for iterating over objects. Here is another using itertools.cycle.

from itertools import cycle

final_c = ['homanif', 'eiesdnt', 'ltiwege', 'lsworara']
final_message = ''.join(next(w) for w in cycle(iter(w) for w in final_c))

edited Feb 13, 2019 at 13:20

answered Feb 13, 2019 at 13:01

Olivier Melançon

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Comments

6502 · Accepted Answer · 2019-02-13 12:48:32Z

2

You can use a nested comprehension:

x = ["homanif", 
     "eiesdnt", 
     "ltiwege", 
     "lsworar"] 

y = "".join(x[i][j]
            for j in range(len(x[0]))
            for i in range(len(x)))

or use nested joins and zip

y = "".join("".join(y) for y in zip(*x))

answered Feb 13, 2019 at 12:48

6502

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1 Comment

Mayukh Nair Over a year ago

@Chris_Rands already gave me the second one-liner code in the comments section instead, which worked really well. Nonetheless, I'll mark this as the correct answer since it has that. Thanks!

SLP · Accepted Answer · 2019-02-13 12:52:43Z

1

Here is a code that works for me :

final_c = ["homanif", "eiesdnt", "ltiwege", "lsworar"]
final_message = ""
current_char = 0

for i in range(len(final_c[1])):
    for c in final_c:
        final_message += c[current_char]
    current_char += 1

# final_message += final_c[0][:-1]    

print(final_message)

I hope it helps

answered Feb 13, 2019 at 12:52

SLP

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Comments

Polaris000 · Accepted Answer · 2019-02-13 12:58:56Z

1

I don't understand what you are expecting with the line final_message += final_c[0][:-1]

The code works just fine without that. Either remove that line or go with something like list comprehensions :

final_message = "".join(final_c[i][j] for j in range(len(final_c[0])) for i in range(len(final_c)))

This gives the expected output:

helloitsmeiwaswonderingafter

answered Feb 13, 2019 at 12:58

Polaris000

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Comments

kederrac · Accepted Answer · 2019-02-13 14:03:16Z

0

looks like you can have a matrix of form nxm where n is the number of words and m is the number of character in a word (the following code will work if all your words have the same length)

import numpy as np

n = len(final_c)  # number of words in your list
m = len(final_c[0])  # number of character in a word

array = np_array(''.join([list(w) for w in ''.join(final_c)])
# reshape the array 
matrix = array.reshape(n,1,m )
''.join(matrix.transpose().flatten())

answered Feb 13, 2019 at 14:03

kederrac

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