Merging arrays with for loop in python-CodePudding

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]

CodePudding user response：

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()

CodePudding user response：

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]

CodePudding user response：

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)

CodePudding user response：

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]

CodePudding user response：

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)

CodePudding user response：

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)

CodePudding user response：

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]