4>
      
          <div id="comment" class="fullcommenttop"><div class="comment cmt"><p>We often need to &quot;reindex&quot; one array/vec/series/frame so as to produce a new
one.</p><p>First, note that an array A of values of type T is actually a mapping defined
as</p><pre>f
[<span class="num">0</span>, A.length) <span class="kw">=&gt;</span> {T}</pre><p>That is, each integer index of the array yields a value of type T when it is
de-referenced.</p><p>ReIndexer has two fields, lTake and rTake, which are ar