如何只显示循环中的第一个<a>并隐藏所有其他元素？

I am using a function

function recursiveArrayToList($array = array()){
        echo '<ul>';
        foreach ($array as $key => $value) {
            echo '<li><a href="#">' . $key . '</a>';
            if (is_array($value)) {
                recursiveArrayToList($value);
            }
            echo '</li>';
        }
        echo '</ul>';
    }
    echo recursiveArrayToList($array);

that creates a ul list.

I want to hide all elements EXCEPT the first <a>. This should be displayed.

I used this solution to detect the first element:

function recursiveArrayToList($array = array()){
    $first = true;
    echo '<ul>';
    foreach ($array as $key => $value) {
        if ( $first )
        {
           echo "first element, that should be shown";
           $first = false;
        }
        else
        {
           echo "all other elements that should be hidden";
        }
        echo '<li><a href="#">' . $key . '</a>';
        if (is_array($value)) {
            recursiveArrayToList($value);
        }
        echo '</li>';
    }
    echo '</ul>';
}
echo recursiveArrayToList($array);

But now all my elements that do have children get the text "first element that should be shown" not only the first element as expected.

I made a mistake in my question, so to be very clear I will show here what I need:

<ul><---- Show only this element
    <li>farm 
        <ul><---- Do not show
            <li>animals</li>
                <ul><---- Do not show
                    <li>horses</li>
                        <ul>
                            <li>fred</li>
                            <li>sam</li>
                            <li>alan</li>
                            <li>john</li>
                        </ul>
                    </li>
                </ul>
            </li>
        </ul>
    </li>
</ul>

And here is my script:

<script>

$(window).load(function(){
    $('li a').click(function (e) {
        e.preventDefault();
        var ullist = $(this).parent().children('ul:first');
        ullist.slideToggle();
    });
});
</script>

CSS

.hidden {
  display: none;
}

PHP

$class = !$first ? "class='hidden'" : "";
echo '<li ' . $class . '><a href="#">' . $key . '</a>';
$first = false;

EDIT

Overall this is what you should have:

function recursiveArrayToList($array = array(), $first = true){
  echo '<ul>';
  foreach ($array as $key => $value) {
    $class = !$first ? "class='hidden'" : "";
    echo '<li ' . $class . '><a href="#">' . $key . '</a>';
    $first = false;
    if (is_array($value)) {
      recursiveArrayToList($value, false);
    }
    echo '</li>';
  }
  echo '</ul>';
}
echo recursiveArrayToList($array);

You can pass a parameter by reference that will indicate if it's the current first element:

function recursiveArrayToList($array = array(), &$first){
    echo '<ul>';
    foreach ($array as $key => $value) {
        if ( $first )
        {
           echo "first element, that should be shown";
           $first = false;
        }
        else
        {
           echo "all other elements that should be hidden";
        }
        echo '<li><a href="#">' . $key . '</a>';
        if (is_array($value)) {
            recursiveArrayToList($value, $first);
        }
        echo '</li>';
    }
    echo '</ul>';
}
$first = true;
echo recursiveArrayToList($array, $first);

Note that I passed $first by reference (hence the & before the parameter name) - This mean that changes in the value of this parameters inside the function will save to the original $first that was declared outside the function scope.

Alternative solution, use a default parameter value to the $first variable:

function recursiveArrayToList($array = array(), $first = true){
    echo '<ul>';
    foreach ($array as $key => $value) {
        if ( $first )
        {
           echo "first element, that should be shown";
           $first = false; // You can comment out this line in order to allow the display of all the first "<li>" on the first level
        }
        else
        {
           echo "all other elements that should be hidden";
        }
        echo '<li><a href="#">' . $key . '</a>';
        if (is_array($value)) {
            recursiveArrayToList($value, false);
        }
        echo '</li>';
    }
    echo '</ul>';
}

echo recursiveArrayToList($array);

Now, when you're calling recursiveArrayToList on the first time, the $first is true by default, and the recursive call is passing false to prevent outputting the string.