var(columnName, population = false) {
        const numericDF = this.df.filter(row => isNumber(row.get(columnName)));
        const mean = this.mean(columnName);
        return (
            Number(
                numericDF.reduce(
                    (p, n) => p + Math.pow(n.get(columnName) - mean, 2),
                    0
                )
            ) /
            (numericDF.count() - (population ? 0 : 1))
        );
    }
Compute the variance into a numeric column.
@param {String} columnName The column to evaluate, containing Numbers.
@param {Boolean} [population=false] Population mode. If true, provide the population variance, not the sample one.
@returns {Number} The variance into the column.
@example
df.stat.var('column1')