Overview
Introduction
Sometimes you need a longer list built from a short repeating pattern, such as generating placeholder test data or padding a dataset to a larger size while keeping its structure.
The List Duplicator takes a list and repeats it end-to-end a chosen number of times, producing one longer concatenated list rather than modifying any individual item.
What Is List Duplicator?
This is a list-generation tool that concatenates N copies of your input list together, in order, using whatever separator you configure.
It treats the input as a single repeating unit; the sequence of items itself is never reordered or altered, only repeated.
How List Duplicator Works
The input is split into items using the chosen separator (newline, comma, or a custom delimiter), then that array of items is repeated N times and flattened into one longer array.
The repeated array is rejoined using the same separator you selected, so a comma-separated input stays comma-separated in the output.
When To Use List Duplicator
Use this when you need a quick way to bulk out a list for test data, sample datasets, or repeated boilerplate entries.
It's handy alongside List Length Changer when you want to pad a list past a certain size, first duplicate it a couple of times, then truncate to an exact length.
Often used alongside List Length Changer, Custom List Creator and List Item Appender.
Features
Advantages
- Preserves the original item order and content exactly, only repeats it.
- Works with any separator style, so it fits comma-separated, newline-separated, or custom-delimited lists.
- Simple, predictable output that's easy to reason about for test data generation.
Limitations
- Only supports whole-list repetition, not per-item repetition.
- Capped at 1000 repeats to keep output size reasonable.
Examples
Best Practices & Notes
Best Practices
- Pick the separator that matches your source data before duplicating, so the output stays consistent with whatever you'll paste it into next.
- If you need a specific final size rather than an exact multiple of your list's length, follow up with List Truncator or List Length Changer.
Developer Notes
Implemented by repeating the parsed items array N times with a simple loop and spreading each copy into a result array, then rejoining with `Array.prototype.join()`-equivalent logic via the shared list separator helper.
List Duplicator Use Cases
- Bulking out a short sample list into a larger test dataset
- Repeating a small set of placeholder values to fill a fixed-size form or spreadsheet column
- Building a repeating pattern list for design mockups
Common Mistakes
- Expecting each individual item to repeat in place ("a,a,a,b,b,b") rather than the whole list repeating in sequence.
- Forgetting to set the repeat count, which defaults to a small value rather than duplicating indefinitely.
Tips
- Combine with List Truncator afterward if you need an exact final item count that isn't a clean multiple of your original list's length.
- Use a custom separator if your downstream tool expects something other than commas or newlines.