Cross-Validation Performance Aggregation with Undefined Values
<p>I wonder what is the correct way to calculate average performance over several folds in cross-validation.</p>

<p>For example, I have 5 folds of F1 with values </p>

<p><code>[0.5 0.3 0.25 null 0.7]</code></p>

<p>What's is the average F1 of this system? </p>

<ul>
<li>I could take null as 0 or just output null as an average result. </li>
<li>Alternatively, I can take only defined four values and divide by 4, but this is not correct either, because if there is some system that did 0.1 on this fold, it's performance will be poorer that the one with null, however, 0.1 is much better that null.</li>
</ul>