title: Yii2 ArrayHelper::map Concatenate third parameter
body: <p>This is my code.</p>
  
  <pre><code>$activities = ArrayHelper::map(LibActivity ::find()-&gt;all(), 'id', 'activity_name');
  </code></pre>
  
  <p>it generates the following.</p>
  
  <pre><code>    &lt;select id="tblncddpvlcccbis-activity_id" class="form-control" name="TblNcddpVlccCbis[activity_id]"&gt;
      &lt;option value=""&gt;---Select Type of Activity---&lt;/option&gt;
      &lt;option value="1"&gt;Social Mobilization&lt;/option&gt;
      &lt;option value="2"&gt;Project Identification/Selection&lt;/option&gt;
      &lt;option value="3"&gt;Project Approval&lt;/option&gt;
      &lt;/select&gt;
  </code></pre>
  
  <p>What I want is to concatenate the third parameter so that the option would be the <code>id-activity_name</code> like this:</p>
  
  <p><code>$activities = ArrayHelper::map(LibActivity ::find()-&gt;all(), 'id', 'id'.'-'.'activity_name');</code></p>
  
  <pre><code>&lt;select id="tblncddpvlcccbis-activity_id" class="form-control" name="TblNcddpVlccCbis[activity_id]"&gt;
  &lt;option value=""&gt;---Select Type of Activity---&lt;/option&gt;
  &lt;option value="1"&gt;1-Social Mobilization&lt;/option&gt;
  &lt;option value="2"&gt;2-Project Identification/Selection&lt;/option&gt;
  &lt;option value="3"&gt;3-Project Approval&lt;/option&gt;
  &lt;/select&gt;
  </code></pre>