Get checked checkboxes from Gravity Forms checkbox field, as array

rs_gf_get_checked_boxes.php

<?php

// 1/3) Usage:
$entry_id = 100; // usually provided in a filter, if so you can remove this line.
$entry = GFAPI::get_entry( $entry_id ); // get the entry, if this was provided in a filter you can remove this line.
$field_id = 35; // field ID can be found when field is selected while editing the form

$value = rs_gf_get_checked_boxes( $entry, $field_id );

// 2/3) Example output:
/*
var_dump($value);
array(2) {
  ["35.4"]=>
  string(12) "Nonprofit Organizations"
  ["35.11"]=>
  string(5) "Other"
}
*/

// 3/3) Function to copy:
/**
 * Return an array of checkboxes that have been checked on a Gravity Form entry.
 * Field keys are the input ID. For example "35.4", which means the 4th item of field #35.
 *
 * @param $entry
 * @param $field_id
 *
 * @return array
 */
function rs_gf_get_checked_boxes( $entry, $field_id ) {
	$items = array();
	
	$field_keys = array_keys( $entry );
	
	// Loop through every field of the entry in search of each checkbox belonging to this $field_id
	foreach ( $field_keys as $input_id ) {
		
		// Individual checkbox fields such as "14.1" belongs to field int(14)
		if ( is_numeric( $input_id ) && absint( $input_id ) == $field_id ) {
			$value = rgar( $entry, $input_id );
			
			// If checked, $value will be the value from the checkbox (not the label, though sometimes they are the same)
			// If unchecked, $value will be an empty string
			if ( "" !== $value ) $items[ $input_id ] = $value;
		}
		
	}
	
	return $items;
}