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

    return sumSimple(x) / x.length;
}
The mean, _also known as average_,
is the sum of all values over the number of values.
This is a [measure of central tendency](https://en.wikipedia.org/wiki/Central_tendency):
a method of finding a typical or central value of a set of numbers.

The simple mean uses the successive addition method internally
to calculate it's result. Errors in floating-point addition are
not accounted for, so if precision is required, the standard {@link mean}
method should be used instead.

This runs in `O(n)`, linear time, with respect to the length of the array.


@param {Array<number>} x sample of one or more data points
@throws {Error} if the length of x is less than one
@returns {number} mean
@example
mean([0, 10]); // => 5