mauss/src/core/array/reduce.js

practical functions and reusable configurations

// aggregations and scans
/**
 * Calculates the mean from a list of numbers using an incremental approach (moving average algorithm), which uses a constant space and updates in constant time. This method helps avoid potential numerical instability issues when dealing with a large sum, such as an integer overflow.
 *
 * @example
 * ```javascript
 * // returns 3
 * average([1, 2, 3, 4, 5]);
 * ```
 */
export function average(numbers) {
    let mean = 0;
    for (let i = 0; i < numbers.length; i++) {
        mean += (numbers[i] - mean) / (i + 1);
    }
    return mean;
}
export function count(array, predicate) {
    if (!predicate)
        return array.length;
    let count = 0;
    for (let i = 0; i < array.length; i++) {
        if (predicate(array[i]))
            count++;
    }
    return count;
}
/**
 * Find the minimum and maximum values in an array of numbers
 */
export function minmax(array) {
    if (!array.length)
        return [0, 0];
    let min = array[0], max = array[0]; // prettier-ignore
    for (let i = 1; i < array.length; i++) {
        min = array[i] < min ? array[i] : min;
        max = array[i] > max ? array[i] : max;
    }
    return [min, max];
}
/**
 * A function that accepts an indexable object.
 * @returns `{ head, last }` of the object
 */
export function sides(x) {
    return { head: x[0], last: x[x.length - 1] };
}
export function sum(array) {
    let total = 0;
    for (let i = 0; i < array.length; i++) {
        total += array[i];
    }
    return total;
}