<p>In <a href="https://github.com/mlpack/mlpack/pull/742#discussion_r73781882">src/mlpack/methods/preprocess/preprocess_describe_main.cpp</a>:</p>
<pre style='color:#555'>&gt; + * @param rowMean Mean of the given vector.
&gt; + * @return Skewness of the given vector.
&gt; + */
&gt; +double Skewness(const arma::rowvec&amp; input,
&gt; +    const double&amp; rowStd,
&gt; +    const double&amp; rowMean,
&gt; +    const bool population)
&gt; +{
&gt; +  double skewness = 0;
&gt; +  double S3 = pow(rowStd, 3);
&gt; +  double M3 = SumNthPowerDeviations(input, rowMean, 3);
&gt; +  double n = input.n_elem;
&gt; +  if (population)
&gt; +  {
&gt; +    // Calculate Population Skewness
&gt; +    skewness = n * M3 / (n * n * S3);
</pre>
<p><a href="https://github.com/stereomatchingkiss" class="user-mention">@stereomatchingkiss</a> I imitated the result from <a href="https://support.office.com/en-US/article/SKEW-P-function-76530A5C-99B9-48A1-8392-26632D542FCB">excel</a><br>
I guess this is equivalent to "direct skewness formula" in the <a href="http://www.macroption.com/skewness-formula/">page</a></p>

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