WordPress at a glance
filter is not described

duplicate_comment_id filter-hook . WP 4.4.0

Filters the ID, if any, of the duplicate comment found when creating a new comment.

Return an empty value from this filter to allow what WP considers a duplicate comment.

Usage

add_filter( 'duplicate_comment_id', 'filter_function_name_3391', 10, 2 );
function filter_function_name_3391( $dupe_id, $commentdata ){
	// filter...

	return $dupe_id;
}
$dupe_id(int)
ID of the comment identified as a duplicate.
$commentdata(array)
Data for the comment being created.

Where the hook is called

wp_allow_comment()
wp-includes/comment.php 660
$dupe_id = apply_filters( 'duplicate_comment_id', $dupe_id, $commentdata );

Where the hook is used (in WP core)

Does not used.