List monthy archives for specific year with wp_get_archives

Question

The year, monthnum, day and w (week) parameters are only used to highlight/pre-select the current item in the list/output and they only take effect on an archive page like date and category archives. And by “highlight”, I mean WordPress will add either selected='selected' (if the format is option) or aria-current="page" (for other format than link) to the output. Something like this (note the selected attribute):

// Assume $results contains database's rows (row objects).
// And '2018' is in the $args you pass to wp_get_archives().
$output="";
foreach ( $results as $row ) {
    if ( is_archive() && '2018' === $row->year ) {
        $output .= '<option value="2018" selected>2018</option>';
    } else {
        $output .= '<option value="2018">2018</option>';
    }
}

Try the following and visit any archive pages, and you’d see the year 2018 option is pre-selected:

$my_archives="<select>" . wp_get_archives( array(
    'type'   => 'yearly',
    'limit'  => 10,
    'echo'   => 0,
    'year'   => '2018',
    'format' => 'option', // this outputs an <option>
) ) . '</select>';

Other examples below, assuming there’s a (public) post on November 1, 2018:

And that you’re on an archive page — on other pages like single posts, those four parameters (year, monthnum, day and w) default to the ones in the main query.

When format is monthly, November 2018 would be pre-selected:

$my_archives="<select>" . wp_get_archives( array(
    'type'     => 'monthly',
    'limit'    => 10,
    'echo'     => 0,
    'year'     => '2018',
    'format'   => 'option',
    'monthnum' => 11,
) ) . '</select>';

When format is weekly, October 29, 2018–November 4, 2018 (week 44^th in 2018) would be pre-selected:

$my_archives="<select>" . wp_get_archives( array(
    'type'   => 'weekly',
    'limit'  => 10,
    'echo'   => 0,
    'year'   => '2018',
    'format' => 'option',
    'w'      => 44,
) ) . '</select>';

When format is daily, November 1, 2018 would be pre-selected:

$my_archives="<select>" . wp_get_archives( array(
    'type'     => 'daily',
    'limit'    => 10,
    'echo'     => 0,
    'year'     => '2018',
    'format'   => 'option',
    'monthnum' => 11,
    'day'      => 1,
) ) . '</select>';

So that year parameter won’t give you the results you’re wanting to have; however, it is possible to achieve the results using the getarchives_where hook in combination with a custom parameter, like so:

This should go in the theme’s functions.php file:

add_filter( 'getarchives_where', function ( $where, $parsed_args ) {
    if ( ! empty( $parsed_args['in_year'] ) ) {
        $year = absint( $parsed_args['in_year'] );
        $where .= " AND YEAR(post_date) = $year";
    }
    return $where;
}, 10, 2 );

Then when you call wp_get_archives(), simply use the in_year parameter to include only the archives for a specific year: (* You can change the parameter name, but also change it above.)
```
$my_archives = wp_get_archives( array(
    'type'    => 'monthly', 
    'limit'   => 10,
    'echo'    => 0,
    'in_year' => '2018', // custom parameter
) );
```
But you can still use the standard year parameter to highlight/pre-select the relevant item.