About

Batch-processing a list through a function is a fundamental operation in data manipulation, yet manual application across hundreds of values invites transcription errors and costs hours. This tool applies a selected transformation f(x) to each element x in your input list, returning the mapped output in O(n) time. It supports over 40 built-in mathematical, string, and type-conversion functions, plus a custom expression mode where you write raw JavaScript using x (current value) and i (index). Filtering functions like isPrime or isEven return boolean masks. Aggregation functions collapse the list into a single statistic. Note: custom expressions execute via new Function() with a capped iteration guard. The tool does not sandbox against all side-effects. Do not paste untrusted code.

Formulas

The core operation is a map transformation applied element-wise across an input list of length n:

output = [f(x₀), f(x₁), …, f(x_n−1)]

For aggregation functions like mean, the result collapses to a scalar:

x = 1n n∑i=1 x_i

Population variance used for variance:

σ² = 1n n∑i=1 (x_i − x)²

Custom expressions receive x (current value) and i (zero-based index) as parameters. The expression is compiled once via new Function('x','i', "return " + expr) and invoked per element. Factorial is computed iteratively: n! = n∏k=1 k, capped at n ≤ 170 to stay within IEEE 754 double precision range.

Reference Data

Category	Function	Input Example	Output Example	Notes
Math	square	5	25	x²
Math	cube	3	27	x³
Math	sqrt	16	4	Returns NaN for negatives
Math	abs	−7	7	Absolute value
Math	factorial	6	720	Max n = 170
Math	log10	1000	3	Base-10 logarithm
Math	ln	2.718	≈1	Natural logarithm
Math	exp	2	7.389	e^x
Math	reciprocal	4	0.25	1 ÷ x
Math	negate	5	−5	−x
Math	double	8	16	2 × x
Math	halve	10	5	x ÷ 2
Math	floor	3.7	3	Round down
Math	ceil	3.2	4	Round up
Math	round	3.5	4	Nearest integer
Math	sign	−42	−1	Returns −1, 0, or 1
String	uppercase	hello	HELLO	Locale-aware
String	lowercase	WORLD	world	Locale-aware
String	capitalize	hello world	Hello World	Each word capitalized
String	reverse	abc	cba	Character reversal
String	length	hello	5	Character count
String	trim	hi	hi	Strips whitespace
String	slugify	Hello World	hello-world	URL-safe format
Type	toBinary	10	1010	Base-2 string
Type	toHex	255	ff	Base-16 string
Type	toOctal	8	10	Base-8 string
Type	toCharCode	A	65	First char code
Filter	isEven	4	TRUE	Divisible by 2
Filter	isOdd	3	TRUE	Not divisible by 2
Filter	isPrime	7	TRUE	Trial division up to sqrt(n)
Filter	isPositive	5	TRUE	x > 0
Filter	isNegative	−3	TRUE	x < 0
Aggregate	sum	[1,2,3]	6	Collapses to single value
Aggregate	mean	[2,4,6]	4	Arithmetic mean
Aggregate	median	[1,3,5]	3	Middle value (sorted)

Frequently Asked Questions

The expression you type is wrapped as the return value of a JavaScript function: new Function('x', "i", "return " + yourExpression). The variable x holds the current list element (auto-cast to a number if numeric), and i is the zero-based index. You can use any standard Math methods, e.g., Math.pow(x, 3) + i. The function is compiled once and invoked per element. A try-catch guards each call, so one failing element won't crash the entire batch - it returns an error marker for that position.

The tool attempts to parse each element via parseFloat(). If parsing fails (returns NaN), mathematical functions propagate NaN for that element, which is displayed as "NaN" in the output. String functions treat the raw string value. Filter functions like isEven return FALSE for non-numeric inputs. This preserves the positional mapping between input and output lists.

JavaScript uses IEEE 754 double-precision floats, which can represent values up to approximately 1.7976931348623157 × 10³⁰⁸. The value 170! ≈ 7.26 × 10³⁰⁶ fits within this limit, but 171! overflows to Infinity. For arbitrary-precision factorials, a BigInt implementation would be required.

Map functions produce a one-to-one output: each input element yields one output element, preserving list length. Aggregate functions (sum, mean, median, min, max, count, range, variance, stdDev) collapse the entire numeric list into a single scalar result. The output area displays this single value with a label indicating the aggregation type.

The tool applies one function per execution. To chain, apply the first function, copy the output, paste it back as input, then apply the second function. Alternatively, use the custom expression mode to compose operations in a single pass, e.g., Math.round(Math.sqrt(x)) combines sqrt and round.

The parser accepts commas, newlines, semicolons, and tab characters as delimiters. Mixed delimiters within the same input are supported. Consecutive delimiters are treated as a single separator (empty elements are skipped). Leading and trailing whitespace around each element is trimmed. This means you can paste a column from a spreadsheet (newline-separated) or a CSV row (comma-separated) directly.