getUsedFactorLevels

Determines the factor levels of a factor type vector
that are actually occuring in it.

Miscellaneous helper functions for and from B. Bischl and
some other guys, mainly for package development.

Bernd Bischl

<dl><dt>x</dt>
<dd>[<code>factor</code>] 
The factor.</dd></dl>

<dl>

<dt>x</dt>
<dd>[<code>factor</code>] 
The factor.</dd>

</dl>