Codeigniter checkbox array

My checkboxes look like this

<div>
    <input type="checkbox" name="fruits[]" value="apple" <?php echo set_checkbox('fruits[]', 'apple'); ?> />
    <input type="checkbox" name="fruits[]" value="banana" <?php echo set_checkbox('fruits[]', 'banana'); ?> />
    <input type="checkbox" name="fruits[]" value="peach" <?php echo set_checkbox('fruits[]', 'peach'); ?> />
</div>

I am using array in the names so that I can populate a text field (via jquery) with the values of the checkboxes I select. I am using a script found on stackoverflow.

function calculate() {

        var fruit = $.map($('input:checkbox:checked'), function(e, i) {
            return e.value;
        });

        $('#fruits').val(fruit.join(',')); //adds values separated by comma to #fruits input 
    }

    calculate();

    $('div').delegate('input:checkbox', 'click', calculate);

So far it works but I'm having trouble setting validation rules for the checkboxes because they all have the same name. I tried..

$this->form_validation->set_rules('fruits[]', 'Apple', 'required|xss_clean');
$this->form_validation->set_rules('fruits[]', 'Banana', 'required|xss_clean');
$this->form_validation->set_rules('fruits[]', 'Peach', 'required|xss_clean');

and used echo form_error('fruits[]'); to display validation error but nothing happens. Ultimately I want to display a checkbox in the state it was submitted, should an error occur on another field in my form. Instead all the checkboxes uncheck. I'm not sure how to fix this.

POST

Array ( [FRUITS] => Array ( [0] => apple [1] => banana [2] => peach )

this is when they are checked

Try without using the square brackets [], so just 'fruits'.

The [] are just to say to the browser "post these values as an array, not a single value, because they're a group", but in PHP you would just approach it as any other value, viz. $_POST['fruits'].

Hope that helps,

All the best, NwN