What happens if an item isn't a number for sum, min, or max?

You get a clear error naming exactly which item (by position and content) isn't numeric, instead of a silently wrong result like NaN.

What does "concatenate" do exactly?

It joins every item together with no separator in between, so ["ab", "cd"] becomes "abcd". If you want a separator between items, use List Editor or just paste your list as-is.

Does "count" count characters or items?

Items. It returns how many items the separator produced, not the total character count of the input.

Can I get the average instead of sum?

Not directly, but you can divide the Sum result by the Count result, both available from this same tool.

List Reducer Online - Reduce a List to One Value

Overview

Introduction

Sometimes you don't need the whole list back, you need one number or string that summarizes it: a total, a count, a minimum, a maximum.

List Reducer collapses a list down to exactly that single value using whichever operation fits your data.

What Is List Reducer?

A fold/reduce operation for lists: choose concatenate, count, sum, min, or max, and get back one value instead of a list.

It shares the same configurable separator as the rest of the List category, so it reads newline-, comma-, or custom-delimited input.

How List Reducer Works

The input is split into items on the resolved separator; concatenate joins them with no delimiter, and count returns how many items resulted from the split.

Sum, min, and max first parse every item as a number (after trimming), and if any item fails to parse, the operation stops and reports exactly which item and position caused the problem.

When To Use List Reducer

Use sum, min, or max on a list of pasted numbers, prices, scores, measurements, to get a quick aggregate without opening a spreadsheet.

Use count to check how many items a separator produced, handy for verifying a paste didn't drop or merge any lines.

Often used alongside List Function Applier, List Editor and List Splitter.

Features

Advantages

Fails loudly and specifically on non-numeric items instead of silently producing NaN or an ignored item.
Covers the five most common list aggregations without needing five separate tools.
Works with any configured separator, so counts and sums are accurate regardless of list format.

Limitations

No average or median operation directly; divide Sum by Count for an average, or use a dedicated statistics tool for median.
Concatenate inserts no separator between items; if you want one, keep your original list instead of reducing it.

Examples

Sum a comma-separated list of numbers

Input

10, 25, 7

Output

Each item is parsed as a number and the three values are added together.

Count items in a newline list

Input

a
b
c
d

Output

Four lines were produced by the newline split, so count returns 4.

Best Practices & Notes

Best Practices

Trim stray whitespace from numeric items first if you're not sure they're clean, sum/min/max trim automatically but visibly broken values still error.
Use List Function Applier's length-as-value option first if you actually want to sum item lengths rather than item values.

Developer Notes

Numeric parsing uses Number(trimmedItem) rather than parseFloat, so partially-numeric strings like "12abc" are correctly rejected as NaN instead of silently truncated to 12.

List Reducer Use Cases

Totaling a pasted list of prices or invoice line items
Finding the minimum or maximum value in a list of scores or measurements
Verifying how many items a paste actually produced after splitting

Common Mistakes

Expecting sum/min/max to skip non-numeric items silently; they error instead, naming the offending item.
Using concatenate and expecting a separator between items; it joins with nothing by design.
Confusing count (number of items) with the character length of the whole input.

Tips

Run Count first to sanity-check your separator is splitting the list the way you expect before summing.
Divide Sum by Count (both from this tool) to compute an average.

List Reducer