Python – Concatenate Strings in the Given Order

When you need to concatenate strings in a specific custom order, you can use simple iteration with index-based access. This technique allows you to rearrange and join string elements according to any desired sequence.

Basic Example

Below is a demonstration of concatenating strings in a custom order −

my_list = ["pyt", "fun", "for", "learning"]

print("The list is:")
print(my_list)

sort_order = [1, 0, 3, 2]

my_result = ''
for element in sort_order:
    my_result += my_list[element]

print("The result is:")
print(my_result)

The list is:
['pyt', 'fun', 'for', 'learning']
The result is:
funpytlearningfor

How It Works

The process follows these steps:

• A list of strings is defined: ["pyt", "fun", "for", "learning"]

• A sort order list [1, 0, 3, 2] specifies the indices in desired sequence

• An empty string accumulates the concatenated result

• Each index from sort_order accesses the corresponding string element

• The accessed strings are appended in the specified order

Alternative Approaches

Using List Comprehension

words = ["hello", "world", "python", "rocks"]
order = [3, 1, 0, 2]

result = ''.join([words[i] for i in order])
print("Result:", result)

Result: rocksworldhellopython

Using join() with Generator

words = ["data", "science", "is", "amazing"]
order = [2, 3, 1, 0]

result = ''.join(words[i] for i in order)
print("Result:", result)

Result: isamazingsciencedata

Practical Example

Here's a real-world example of reordering date components −

date_parts = ["2024", "12", "25"]
# Convert from YYYY-MM-DD to DD-MM-YYYY format
order = [2, 1, 0]
separator = "-"

formatted_date = separator.join([date_parts[i] for i in order])
print("Original format:", "-".join(date_parts))
print("Reordered format:", formatted_date)

Original format: 2024-12-25
Reordered format: 25-12-2024

Conclusion

String concatenation in custom order is achieved by using an index list to specify the sequence. Use join() with list comprehension for cleaner, more efficient code when dealing with multiple strings.