How to copy one array element value into another with jQuery

I have a text input with a name first_name[120] (predefined key), and I would like to copy the value into another first_name[different predefined key] field with a click of a button.

There may be other first_name[different predefined key] fields in the form so I need the flexibility to make this work for the rest. Any suggestions?

EDIT:

Sorry, I think I need to give a little more information.

The form has a list of fields for gift recipient(s) information. There may be multiple gifts listed in the form, with each one having its own fieldset for entering the gift recipient's info. Basically, I am trying to make a "Copy info from above" feature for subsequent gift recipient fields in the form.

EDIT 2:

This is my solution and it works. Please suggest improvements if possible. It is actually bound to a dropdown with a list of all gifts. So the code knows 开发者_开发百科which section to pull the info from and where to drop it based on the id of the dropdown (e.g. 123|130).

   $('.copy_info').live('change', function(){

    var ids = $(this).val().split('|');

    var from = ids[0];
    var to = ids[1];

    $('#form_fields-' + from + " :input").each(function(){

        var name = $(this).attr('name');
        var new_name = name.replace(/[\d+]/,to);

        $('#form_fields-' + to + ' input[name="' + new_name + '"]').val($(this).val());

    });

});

$('button').click(function() {
    $('input[name="first_name[xxx]"]').val($('input[name="first_name[120]"]').val());
});

xxx is the number of the first_name key you are copying 120 into.

Also remember you can access the specific button that was clicked with this or wrap it in a jQuery object with $(this) to target more specifically the input you are selecting to manipulate.