This function was ported from the RMetrics package
fUtilities to eliminate a dependency on fUtiltiies being
loaded every time. The function is identical except for
the addition of checkData and column
support.
$$Skewness(moment) =
\frac{1}{n}*\sum^{n}_{i=1}(\frac{r_i -
\overline{r}}{\sigma_P})^3$$
$$Skewness(sample) =
\frac{n}{(n-1)*(n-2)}*\sum^{n}_{i=1}(\frac{r_i -
\overline{r}}{\sigma_{S_P}})^3$$
$$Skewness(fisher) =
\frac{\frac{\sqrt{n*(n-1)}}{n-2}*\sum^{n}_{i=1}\frac{x^3}{n}}{\sum^{n}_{i=1}(\frac{x^2}{n})^{3/2}}$$
where $n$ is the number of return, $\overline{r}$
is the mean of the return distribution, $\sigma_P$ is
its standard deviation and $\sigma_{S_P}$ is its
sample standard deviation