Overview
Introduction
Data pipelines and forms often expect a list of an exact, fixed size, but real input rarely lines up perfectly, it's usually a little too short or a little too long.
The List Length Changer resizes any list to precisely the target count in one step, padding with a filler when it's short or truncating when it's long.
What Is List Length Changer?
This is a list-resizing tool: give it a target item count and it either extends or shrinks your list to match exactly, every time.
Padding can be a fixed repeated value or an indexed value with a running number appended, and truncation always trims from the end of the list.
How List Length Changer Works
The input is split into items using your chosen separator, then compared against the target length.
If it's shorter, filler items are appended one at a time (either the raw filler value, or the filler value with the new item's position number appended) until the target length is reached; if it's longer, `Array.prototype.slice()` keeps only the first `targetLength` items.
When To Use List Length Changer
Use this when a downstream system or spreadsheet expects an exact row/column count and your source list doesn't naturally match it.
It pairs well with List Truncator when you only ever need to shrink (never pad), and with List Duplicator when you want to grow a list by repeating its own content instead of a filler.
Often used alongside List Truncator, List Duplicator and Empty List Creator.
Features
Advantages
- Handles both growing and shrinking a list in a single tool with a single target-length input.
- Indexed filler mode produces unique placeholder values instead of identical repeats, useful for IDs or labels.
- Deterministic, no randomness involved.
Limitations
- Truncation only removes items from the end; there's no option to trim from the start.
- Indexed filler numbering restarts based on final list position, not a custom starting number.
Examples
Best Practices & Notes
Best Practices
- Use indexed mode whenever the padded values need to be distinguishable from each other, like placeholder IDs.
- If you need to keep the last N items instead of the first N when shrinking, use List Truncator's direction toggle instead.
Developer Notes
Padding pushes items one at a time in a loop using each new item's 1-based position for indexed mode; truncation is a single `Array.prototype.slice(0, targetLength)` call.
List Length Changer Use Cases
- Filling a spreadsheet column out to a fixed number of rows before import
- Normalizing multiple lists to the same length before zipping or comparing them
- Generating a fixed-size batch of test values from a shorter seed list
Common Mistakes
- Expecting truncation to remove items from the start rather than the end.
- Using repeat mode when unique placeholder values were actually needed, producing identical filler items instead.
Tips
- Set the filler to an empty string with repeat mode if you just want blank placeholder slots, similar to Empty List Creator.
- Check List Length Finder first if you're not sure how far off your current list is from the target.