snapmetrics/dist/stats.js

Lightweight library for tracking real-time metrics and events with rolling statistics over configurable time windows.

/**
 * Calculates the average of an array of values
 * @param values Array of values
 * @param sum Optional pre-calculated sum
 * @returns Average value or null if array is empty
 */
export const calculateAverage = (values, sum) => {
    if (!values.length)
        return null;
    const total = sum ?? values.reduce((a, b) => a + b, 0);
    return total / values.length;
};
/**
 * Calculates percentile using Hyndman and Fan type 7 linear interpolation.
 * @param sortedValues Array of sorted values
 * @param percentile Percentile to calculate (0-100)
 * @returns Interpolated percentile value
 */
export const calculatePercentile = (sortedValues, percentile) => {
    if (!sortedValues.length)
        return null;
    if (sortedValues.length === 1)
        return sortedValues[0];
    const p = percentile / 100;
    const h = (sortedValues.length - 1) * p + 1;
    const hFloor = Math.floor(h);
    if (h === hFloor) {
        return sortedValues[hFloor - 1];
    }
    const hCeil = Math.ceil(h);
    const lower = sortedValues[hFloor - 1];
    const upper = sortedValues[hCeil - 1];
    return lower + (h - hFloor) * (upper - lower);
};
/**
 * Finds the minimum value in an array
 * @param values Array of values
 * @returns Minimum value or null if array is empty
 */
export const calculateMinimum = (values) => values.length ? Math.min(...values) : null;
/**
 * Finds the maximum value in an array
 * @param values Array of values
 * @returns Maximum value or null if array is empty
 */
export const calculateMaximum = (values) => values.length ? Math.max(...values) : null;
/**
 * Calculates the standard deviation of an array of values
 * @param values Array of values
 * @param mean Optional pre-calculated mean
 * @returns Standard deviation or null if array is empty
 */
export const calculateStandardDeviation = (values, mean) => {
    if (!values.length)
        return null;
    const avg = mean ?? calculateAverage(values);
    const squaredDiffs = values.map((value) => Math.pow(value - avg, 2));
    const variance = squaredDiffs.reduce((a, b) => a + b, 0) / values.length;
    return Math.sqrt(variance);
};