Hello,
I’m using PikList for WordPress and for some reason, I’m having trouble to add checkboxes and produce a clean output.
Basically, I created a meta-box “purchase-links” to a custom type “Books”. It looks like this:

My code looks like this:

piklist('field', array(
	'type' => 'group'
		,'field' => 'purchases'
		,'columns' => '12'
		,'label' => __('Purchase links') 
		,'fields' => array(
			array(
				'type' => 'group'
				,'field' => 'shop'
				,'add_more' => true
				,'fields' => array(
					array(
						'type' => 'select'
						,'field' 		=> 'shop_id'
						,'value' 		=> 'amazon'
						,'columns' => '12'
						,'attributes' => array(
						  'class' => 'text'
						)
						,'choices' => array(
						   'amazon' 	=> 'Amazon'
						  ,'kobo' 		=> 'Kobo'
						  ,'chapters' 	=> 'Chapters Indigo'  
							)
						)
					,array(
						'type' => 'checkbox'
						,'field' => 'format'
						,'columns' => '12'
						,'attributes' => array(
						  'class' => 'text'
						)
						,'choices' => array(
						  'paper' => 'paper'
						  ,'ebook' => 'ebook'
						  ,'aubiobook' => 'audiobook'
						)
					)									
					,array(
						'type' => 'text'
					    ,'field' => 'url'
						,'label' => 'URL'
						,'columns' => '12'	
							,'attributes' => array( 
								'placeholder' => 'URL'
							)	
					)
				)
			)
		)
	));	

It kind of works, but I don’t really understand the output it produces for the checkboxes. There’s an extra “array”, and I don’t understand why there is null entries in those arrays. Here is the r_print() of a “shop”:

Array
(
    [shop_id] => Array
        (
            [0] => amazon
        )

    [format] => Array
        (
            [0] => Array
                (
                    [0] => paper
                    [1] => 
                    [2] => ebook
                    [3] => aubiobook
                )

        )

    [url] => Array
        (
            [0] => http://www.amazon.ca/Pride-Prejudice-Jane-Austen/dp/0486284735/ref=sr_1_1?ie=UTF8&qid=1420671439&sr=8-1&keywords=jane+austen+pride+and+prejudice
        )

)
Array
(
    [shop_id] => Array
        (
            [0] => kobo
        )

    [format] => Array
        (
            [0] => Array
                (
                    [0] => 
                    [1] => ebook
                )

        )

    [url] => Array
        (
            [0] => http://store.kobobooks.com/en-CA/ebook/pride-and-prejudice-84
        )

)
Array
(
    [shop_id] => Array
        (
            [0] => chapters
        )

    [format] => Array
        (
            [0] => Array
                (
                    [0] => paper
                    [1] => 
                    [2] => ebook
                    [3] => aubiobook
                )

        )

    [url] => Array
        (
            [0] => http://www.chapters.indigo.ca/books/pride-and-prejudice-penguin-classics/9780143105428-item.html?ikwsec=Home&ikwidx=1
        )

)

Did I do something wrong that it produces this extra array and null entries for the checkboxes (“format” field)?
And in general, is it normal that Piklist produces so many arrays or is it something I do wrong? For a simple text field (like “url”), I didn’t expect it to produce an array containing one entry. Or is each metabox field contained in an array anyway?

Thank you for your help, and don’t hesitate to ask me if I’m not too clear.

Angélique