class="hasAnchor" id="value"><a class="anchor" href="#value"></a>Value</h2>

    <p>A character vector containing the group names. If there are no
        groups, return NA.</p>
    <h2 class="hasAnchor" id="details"><a class="anchor" href="#details"></a>Details</h2>

    <p>All current group codes must be found in the keys, i.e. there can't be
missing values. Argument <code>value</code> can, however, contain keys that are
not in the current group codes.</p>
    <h2 class="hasAnchor" id="see-also"><a class=