Merging arrays with for loop in python

Question

I want to merge two arrays in to one array in an alternating sequence (arr1,arr2,arr1,arr2,....). After two hours i got this far by trying different methods like concatenate or append or two interlocked "for loops".

As i want to use this regardless of the format (string or integer arrays) i wanted to use a "for loop". My try gives me the correct order, but has some elements missing as the counter isn´t perfect. So what can i do correct that?

Example:

arr1 = [1,3,5,7,9,11,13,15,17,19,21,23,25,27,29]
arr2 = [2,4,6,8,10,12,14,16,18,20,22,24,26,28,30]
merged = [None]*2*len(arr1)
v = range(0,len(arr1))
for i in v[::2]:
    merged[i] = arr1[i]
    merged[i+1]=arr2[i]

print(merged)

gives [1, 2, 5, 6, 9, 10, 13, 14, 17, 18, 21, 22, 25, 26, 29, 30, None, None, None, None, None, None, None, None, None, None, None, None, None, None]

merged = [x for tpl in zip(arr1, arr2) for x in tpl]

Matiiss
– Matiiss

2022-09-20 11:26:19 +00:00
Commented Sep 20, 2022 at 11:26 — Matiiss
– Matiiss, Commented Sep 20, 2022 at 11:26

Ajay Pun Magar · Accepted Answer · 2022-09-20 11:29:56Z

1

You can simply merge array by using addition operator for example

result_array=array1+array2

Then you can sort it to get your result

result_array.sort()

edited Sep 20, 2022 at 11:29

answered Sep 20, 2022 at 11:28

Ajay Pun Magar

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4 Comments

Matiiss Over a year ago

they want to interlace the values

Ajay Pun Magar Over a year ago

seems like i am so impatient. I need to slow down.

Matiiss Over a year ago

sorting is not really the answer... it may work in this particular case but it's obviously not a reliable way to achieve what's expected

Ajay Pun Magar Over a year ago

Yes I am aware of that, I need to write another one to make it work but you posted the right one already.

Saad Rehman · Accepted Answer · 2022-09-20 11:34:35Z

0

This could easily be achieved like this:

result = [];
arr1 = [1,3,5,7,9,11,13,15,17,19,21,23,25,27,29]
arr2 = [2,4,6,8,10,12,14,16,18,20,22,24,26,28,30]

for i in range(len(arr1)): 
    result.append(arr1[i]) 
    result.append(arr2[i]) 
    
print(result)

answered Sep 20, 2022 at 11:34

Saad Rehman

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Comments

Matiiss · Accepted Answer · 2022-09-20 11:32:19Z

0

To merge them such that the values alternate you can simply zip the two lists and iterating over the zipped object will return a tuple with an item from one list and an item at the same index from the other list (order of passing arrays to zip is important) and you can extend your list by that returned tuple:

arr1 = [1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29]
arr2 = [2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30]

merged = []
for values in zip(arr1, arr2):
    merged.extend(values)

Alternatively you can use a simple list comprehension:

merged = [x for tpl in zip(arr1, arr2) for x in tpl]

answered Sep 20, 2022 at 11:32

Matiiss

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Comments

Guy · Accepted Answer · 2022-09-20 11:34:36Z

0

Keeping with your solution you need to iterate up to the size of the target list, not the smaller one. You also need to divide i by 2 to fit arr indices

arr1 = [1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29]
arr2 = [2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30]
merged = [None] * 2 * len(arr1)
for i in range(0, len(merged) - 1, 2):
    merged[i] = arr1[i // 2]
    merged[i + 1] = arr2[i // 2]

print(merged)
# [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]

answered Sep 20, 2022 at 11:34

Guy

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Comments

Sachin Kohli · Accepted Answer · 2022-09-20 11:35:58Z

0

Above solutions works;

Another way to get desired result is;

arr1 = [1,3,5,7,9,11,13,15,17,19,21,23,25,27,29]
arr2 = [2,4,6,8,10,12,14,16,18,20,22,24,26,28,30]
merged = []
for i in range(0,len(arr1)):
    merged.append(arr1[i])
    merged.append(arr2[i])
print(merged)

answered Sep 20, 2022 at 11:35

Sachin Kohli

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1 Comment

Phasco Over a year ago

Thanks. I tried a variant from another comment wihich is similar to yous and that works.

Eftal Gezer · Accepted Answer · 2022-09-20 11:40:11Z

0

arr1 = [1,3,5,7,9,11,13,15,17,19,21,23,25,27,29]
arr2 = [2,4,6,8,10,12,14,16,18,20,22,24,26,28,30]
merged = []
[merged.extend([a1, a2]) for a1, a2 in zip(arr1, arr2)]
print(merged)

answered Sep 20, 2022 at 11:40

Eftal Gezer

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Comments

user1877600 · Accepted Answer · 2022-09-20 11:53:55Z

0

You can also use numpy, combination of vstack and flatten

import numpy as np
arr1 = np.array([1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29])
arr2 = np.array([2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30])
result = np.vstack((arr1, arr2)).flatten("F")

print(result)

Result:

[ 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]

answered Sep 20, 2022 at 11:53

user1877600

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