Question

i want use append for first $class, how is it?

var $class =  '.' + $(this).closest('div.find_input').find('div').attr('class');

$(this).closest($class).find('.adda:first-child .mediumCell').append('<a href="" class="add_input"></a>')

EDIT: this my full code:

$('a.remove_input').live('click', function (event) {
                event.preventDefault();
                var $class =  '.' + $(this).closest('div.find_input').find('div').attr('class');
                $(this).closest($class).prev().find('.adda .mediumCell').first().append('<a href="" class="add_input"></a>')
                $(this).closest($class).remove();
            });

html:(i use of several html and several $class)

<div class="column find_input">
    <div class="add_units">
        <div class="mediumCell">
            <input type="text" name="price" placeholder="hello" class="numeric" style="width: 70px;">
        </div>
        <div class="column adda" style="margin: 5px 1145px 0 0; position: absolute; float: left;">
            <div class="mediumCell">
                <a href="" class="add_input">add</a>
            </div>
        </div>
    </div>
</div>

Answer 1

Well to select the first element of a set of matched elements just use first().

$(yourselector).first().doStuff(); 

Doc is here: http://api.jquery.com/first/

The following should add the link to the first $class only:

$('a.remove_input').live('click', function (event) {
    event.preventDefault();
    var $class = '.' +  $(this).closest('div.find_input').find('div').attr('class');
    $($class).first().find('.adda .mediumCell').append('<a href="" class="add_input">add</a>')
    $(this).closest($class).remove();
});