function rootMeanSquare(x) {
    if (x.length === 0) {
        throw new Error("rootMeanSquare requires at least one data point");
    }

    let sumOfSquares = 0;
    for (let i = 0; i < x.length; i++) {
        sumOfSquares += Math.pow(x[i], 2);
    }

    return Math.sqrt(sumOfSquares / x.length);
}
The Root Mean Square (RMS) is
a mean function used as a measure of the magnitude of a set
of numbers, regardless of their sign.
This is the square root of the mean of the squares of the
input numbers.
This runs in `O(n)`, linear time, with respect to the length of the array.

@param {Array<number>} x a sample of one or more data points
@returns {number} root mean square
@throws {Error} if x is empty
@example
rootMeanSquare([-1, 1, -1, 1]); // => 1